Opened Library, CTRL+L, and it looked weird. Couldn't interact with it, couldn't move it on the screen or enter a search. Didn't take a screen shot of it, didn't think about it at the time. Have opened the Library this way hundreds if not thousands of times, just thought it was odd. So closed it. CTRL+L again and below is a snapshot, you won't notice anything until you see the 2nd snapshot.
But notice there are no selections anywhere that would limit the items shown. This snapshot shows it appearing as normal, i.e. border in place, movable on the desktop, etc. Closed & reopened the now floating window a number of times of times and still heart attack time, thousands of mytags were missing.
So, opened the hamburger menu and all mytags still all showed, selected one and voila it provided the expected results, the screen changed to reflect a tag that was not previously shown in the 1st snapshot. Cleared the selection from the pick list by selecting All and now mytags were all back.
Don't know if this is a bug or not. Have performed CTRL+L to open the library a lot since the last release/update. So don't know what's up.
Thought I'd share the experience and sequence. Next time, if it ever happens again, plan on trying to cycle thru the resorting of the column My Tag which, I'm thinking, causes a reread/requery of the data and tags.
Please advise.