This has been going on for over a year now--about once every month or two--and it is extremely annoying (along with Accordance losing font settings, which I just posted here).
For some reason, while doing nothing more than clicking down through search results in BHS-T, Accordance suddenly dropped one of my prominent user Bibles out of a custom group displayed in the Text Browser. One second it was there, and the next second it was gone. See attached.
Now, in similar time-wasting annoyance to the font setting problem, I have to go to the Library and manually add back this Bible to about half a dozen custom groups that I have (and sort it where I want it in that group).
Can we please make these time-wasting problems stop? It's not the first time. I'm sure you wouldn't want to have to redo things over and over again.