While nosing around I found this:
" * The *.sig files contains the PGP signature computed while bundle compilations.
They can be used to verify if bundles files downloaded are the right ones or not."
Copy/Pasted from the READ ME at the top of the untested Beta page.
I just finished installing 6.0.0 Beta3
I restarted the machine just for good measure.
I opened digiKam, performed an investigation, and…, alas…, the problem is still there.
Something about my digiKam installation has to have gotten corrupted or compromised somehow; as, this problem only made itself known just a few hours prior to my starting this thread.
So long as each new install of digiKam overwrites the previous version, my problem just goes along for the ride.
I hate to think about completely purging digiKam and starting anew, but I am afraid that without digging into the “registry” of digiKam, that may be my only option.
I did find out some curious behaviors regarding the missing and partially present thumbnails; Let’s say I searched a tag that has a dozen images; the first two show up intact; the next two only have a portion of the very top showing; the remaining eight thumbnails, although not showing up, have blank positions where they should be.
I can right-click an empty spot and maybe four of the missing thumbnails will magically appear, but I cannot do anything with them.
If I left-click the thumbnail, a small white rectangle will appear on the thumbnail; each time I left-click, another little white rectangle appears.
If, after right-clicking and some of the missing thumbnails appear, I can right-click again and lose them again.
You can try closing digikam, renaming thumbnails.db to thumbnails.db_backup, restarting digikam and let it run for a while to regenerate thumbnails. The .db file should be there main digikam database is.
I did that.
The original thumbnail DB was 1,735,552 KB; the new one is 25,884 KB.
I did manage to lose about a fourth of my Album thumbnails in the process.
I sort of had high hopes for this fixing things; but, alas…, the problem remains.
Although this is affecting many hundreds of images and it is hard to see and remember them all, on the tag searches that I do remember, it is always the same thumbnails that have the problem.
And, although I may find out to the contrary, thus far, it only seems to be affecting the tops of the tag hierarchies.
For instance, if I have a tag “cars”, and within that are sub-tags “red car”, “blue car”, and “green car”, with each of those having their own sub-tags.
I can click to show all of the cars and maybe half of them will not display, even though the information in each of the blue album separator bars will display the correct number that should be there.
If I click “cars” and there are seven “red cars” missing, I can click “red cars” and there they will be.
I never realized how much I used the tag search until it started having this problem.
What would be the outcome if I delete (hide) all of the DBs ?
Will it be like starting at the very beginning ? (hopefully not)
If bad things happen, can I just replace the DBs and be back to where I was ?
https://www.ryananddebi.com/2016/01/04/linux-digikam-editor-not-showing-images/
Read the first comment by FranZ
Yeah you are safe as long as you have backups.
I suggest you file a bug on KDE bugzilla / digikam. Screenshots, screencasts and debug logs will help developers understand the problem faster.
I guess the debug logs is where that Debug View I downloaded a few days ago will come into the picture, right ?
I really like digiKam, but when it hits a snag, it can sure be aggravating to figure out.
But that is true of all software, free, paid or otherwise 
You are correct. You can simply run Debug View and then open digikam and then you will see digikam messages showing up in DebugView.
Yesterday I had an issue with thumbnails too. I was in Preview mode and showed Thumbbar (Ctrl + T) which I normally keep hidden. Thumbnails in the thumbbar never show up (I just saw empty rectangles). When I switched back from Preview to Thumbnails view I noticed that some of the thumbnails were missing completely and some were missing partially. I just restarted digikam and the problem went away. Of course I did not have Debug Veiw running so I have no idea what exactly happened.
Well, I finally submitted my bug report; I hope that I did things correctly.
Bug report # 401542
I included three screenshots.
I made several attempts at getting a DeBug View that made sense, but I don’t seem to be smart enough to use it.
DeBug View also gives me a failed warning when I try to do the Kernel-Mode thing.
I did manage to get pages and pages of Win32 Output concerning digiKam; I perused the entire log and found no mention about the tag searches I did while it was running.
Whatever my problem is, it is growing exponentially; whereas a few days ago I had a few dozen missing thumbnails, now I have hundreds, if not thousands.
Curiously, I have discovered that I can execute Screen Capture from FastStone and ALL of my missing thumbnails will magically re-appear; the same also happens when I press the Windows key; however, I cannot do anything useful with these re-appeared thumbnails.
Wherever I left-click on the re-appeared thumbnails,a white rectangle will appear and remain; with every click, I add another rectangle.
I have discarded and rebuilt the thumbnail database several times to no avail.
I backed up the entire database, deleted it, and started digiKam and it was as if it were a fresh virgin install with all of my meticulous tag heirarchy and album collections gone.
I re-instated the old database and was back to where I was and still with the problem.
Thank you very much for submitting the bug report. I am afraid your issue might has something to do with hardware drivers, etc. It is just a guess though…
I have just performed a random but very thorough search through Album View and did not find a single missing or uncooperative thumbnail.
Thus far, I had never even experimented with any of the other tabs on the left pane – only ever using Albums view and Tags view.
I just did investigate all of the other tabs; and, there did seem to be quite a few missing thumbnails in those views as well.
I have not added any new hardware in ages and have had Windows Updates turned completely off for a long time, so I cannot blame this on some update or other.
I use the Tags view almost daily and did not experience this problem prior to my first posting about it; but, once it has started giving problems, it seems like a landslide.
I may or may not have already made note of this: Let’s say for example in Tags view I click on the top tag in the Trucks heirarchy and see that there are seven Peterbilt thumbnails not displaying; I might click on Peterbilt and there they will display fine; or, I am also having it happen the other way around; all thumbnails may be showing under the top tag and several missing under the sub-tags.
I have also noticed that, once a thumbnail goes missing, it will stay missing; it won’t be missing one time and show up the next.
I have spent countless hours meticulously building my tag tree and have several thousands of images tagged; I sure hope this can be fixed without me having to start all over from scratch.
Have you made a backup and checked your disk for bad sectors?
Yes; no problems found.
I honestly don’t think this is a hardware or driver related problem.
I am not experiencing any difficulties anywhere else, not even in digiKam.
I have now found a new erratic behavior in Tags view, of which I have added a screenshot and more information to my bug report.
In this new situation, the information on the blue bar says 3 Items while at the same time it is displaying 4 Items and there should be 8 Items.
Each time I investigate Tags view, more thumbnails are missing and now there is also erroneous information.
It is as though my digiKam database has developed a self-destructing worm or virus within itself.
In the Tag Manager, there is a menu Sync Export; in this menu is a command “Wipe All Tags from Database ONLY”
There is also a command “Read Tags from Image”
What would be the outcome if I HiLite the very top of the tag tree “Tags”, click “Wipe All Tags”, restart digiKam, and then HiLite “Tags” and click “Read Tags from Image”
To my way of thinking, this should force digiKam to start afresh so far as tags to image associations.
What are your thoughts on this ?
Sounds like a lot of work! Please make a backup of everything of this is the route you choose to go.
I hid the actual database folder and made an empty one.
I started digiKam and the first thing it asked was for me to add a collection (folder)
I added three varied folders, thus three Albums/Collections with a total of 24 jpeg image files.
Each file had three or more keyword tags embedded within – all tags had been applied with digiKam prior to this test.
When digiKam then went ahead and opened, all of the tags were distributed in the same heirarchic order that I had created in the old database – except for the little tag picture/icons; = so far, so good.
In Tags View, I opened Tag Manager, clicked Wipe All Tags from the Database; immediately, the Tag Manager disappeared and both tag panels went blank, as if no tag tree had ever been created.
In order to bring up the Tag Manager again, I had to switch to Albums view.
I counted twenty alligators and clicked “Read Tags from Image”
In about half-a-minute, all of my tag tree structure was recreated as if it had never been anywhere.
So far, more so good.
Is there any way that digiKam can show me how many total image files that I have associated with it ?
I know it is a lot.
I am wondering just how long it would take to do this for the whole works.
This behavior depends on how you set digikam to write metadata. You can write to either database only or to database and JPEGs themselves or to database, JPEGs and XMP sidecars.
Digikam 6.0.0 beta detects changes in sidecars on startup.
I have digiKam set to always write tags and geolocation into the jpeg.