I highlighted jpgs & raws that could share the same caption, typed in the caption in the right pane, then hit Apply. That worked fine for awhile.
I can add captions to some raw files, but not others. I captioned this raw file just now:
If you select both ARW and JPG - right click - group by filename and then click on the group - add a caption. Does digikam ask you whether to apply changes for each file or only to the one which is on the top of the stack?
It doesn’t ask for a choice. It only captions the jpg when captioning the filename group.
Perhaps I’d better figure out how to use DebugView.
Another piece of the puzzle: in some albums, raw captioning works fine; in other albums, can’t caption (but can title, tag, & star rate).
DebugView is very easy to use.
Hope this was okay, but I cleared the DebugView log, then attempted to write a caption to a raw file in digiKam. So this should just show what happens during a failed caption attempt:
Are these of any help? The Dublin Core description field in XMP is blank in the unsuccessful raw caption, but contains text in the successful raw caption.
If I open the XMP file in Notepad, and type in:
dc:description
rdf:Alt
<rdf:li xml:lang=“x-default”> Ferry view on the way to Shelter Island; eastern Long Island Sound</rdf:li>
</rdf:Alt>
</dc:description>
the caption shows up in the raw file thumbnail in digiKam. Don’t want to do this for several hundred raw files, though. 
You are using digikam version 6.0.0, right? Just confirming. Have you tried deleting / renaming xmp sidecar and add captions again?
Also, you settings- metadata- advanced. Have you changed anything there? (You should not)
I see “wroteComment : false”
Ism wondering why is that…
Could you share a sample image by chance? Any raw file which digiKam can’t add a caption to will do.
Yes, using 6.0.0. No metadata-settings-advanced changes.
Renaming old xmp sidecar & creating a new one worked.
The DeBugView still shows “wroteComment=false” even though my captions now show for the raw file.
Well, the captioning is getting wonkier & wonkier. I accidentally gave the raw file a star rating, and that wiped out my caption. I tried giving my jpg a star rating, and THAT wiped out the captioning too.
Not sure why the write caption feature is so fragile. I’d written captions for 2500 files and many of the captions are missing now. Would it help to download a new digiKam to see if its caption feature works better?
It probably DOES have to do with “wroteComment: false”.
Well, if you are using 6.0.0 release (not beta) it is the newest stable version available.
I would suggest to create a bug report in bugzilla. The developers will ask for sample raw files though.
I don’t think I ever changed any advanced setting in Metadata section. But it won’t hurt to try. Please back up your images and the database files before doing that though.