I tag all resources in my library - especially the PrintLibrary works, so I know whether I own them in Logos and where to look for the non-Logos resources (Kindle, paper library shelves...). Tagging also indicates topical content, e.g. which bible books are commented on - so I was perplexed when I found that a large portion of my PintLibrary books, 117 of them, lost their tags in 10.1. Beta 3.
Those 117 now tag-less works all are license:none books, but not all of those

That's how it looks in Verbum 10.0 SR-2 (I'm so glad the deletion of the mytags has not synced over):

After a bit of testing I found that adding mytags in Beta 3 to such a tag-less resource would sync over to SR-2 (overwriting previously existing tags) and adding another mytag in the SR-2 library would sync all mytags of that resource over to Beta 3, thus I could salvage my data in this way.
EDIT: this is how it looks now in Beta 3:

Deleting the tags seems not to occur at subsequent restarts. /EDIT
Logs (noting I restarted Logos, so I have no log of the first run under Beta 3, but I include install logs):
Please prevent this from happening again!