Annoying popups

My linux desktop is always on and logged in.
Since a couple of days, [I presume since a keybase update was applied] each morning I find a couple of pop-ups "You accessed a public folder" on my screen. This may be the result of some file system scan that is executed nightly, but I never got these pop-ups, and --scaringly-- some of the pop-ups involve people that I totally do not know.

What is going on?

No files, tests, or entry points are named. Start by reproducing the unexplained public-folder pop-ups on an always-on Linux desktop and compare their timing with the reported Keybase update or nightly filesystem scan; done means identifying the trigger and documenting or fixing the unexpected notifications.

Written by the indexing model from the issue text.