It is a really bad error of darktable 2.6.0, anyone with the same problem? Any idea to solve it?
P. S.: I use the Windows version.
I had this for a while too, however I was unable to reliably reproduce it. Opening and closing the application and clearing the collect images criteria fixed the problem.
Thanks for your answer but, unfortunately, I tried that several times and did not work.
Looks like a Windows specific issue, cannot reproduce on Linux.
I solved it. I deleted all the files in User\AppData\Local\darktable. It was a bit annoying though, all my customizations and my library were gone, I’ll have to do everything again.