Since Monday 10/26 I found that our document libraries do not display UI for term selector from the "tags" icon. Instead of a tree, they show only the title of the given term set.
This affects Modern Communication site and Team sites in our tenant with different designs applied. Checked with Edge, Chrome, and Firefox.
Appears to be the element div.TaxonomyTreeSelector that is blank, but I don't have any functioning elements to compare it to.