macOS Big Sur: Finder Randomly Depopulates Favorites in Sidebar

macOS Big Sur Finder
A few days ago, I was baffled by the disappearance of an item from the sidebar of Finder windows. I shrugged, and re-added it.
Today, my Favorites sidebar was mostly wiped out, with half of its entries just gone.
So it seems that the Finder (or something in macOS) is sporadically wiping out entries on the Favorites area of the sidebar
These entries are used in Finder windows but also in the Save/Open dialogs, and they save me a lot of time navigating around. So it’s not a minor thing, it directly impacts my workflow.
Then there is the sidebar itself, which when it’s not losing entries is a major nuisance in itself, that is, reappearing constantly even though I’ve hidden it (Finder windows).
Dozens of little quirks and problems like this that make macOS increasingly irritating to use. We have not seen any real usability progress for what now... a decade?