just to be 100% sure, can you please confirm that you haven’t changed the Abandoned Plugins/Themes Tolerance setting in the MainWP > Settings, and can you please check if you Ignored some abandoned in the meantime?
I thought maybe it was because it was updated SO long ago (1314 days), but Force Regenerate Thumbnails was updated 1973 days ago, so it must not be that.
I also don’t see any connection or difference between the site that shows the 1 abandoned plugin and the other sites. Several are on the same host.
I have been monitoring my dashboard and I couldn’t duplicate this behavior.
But it crossed my mind that if some of your child sites drop the connection and get reconnected again, the abandoned items data could be removed when the connection drops and it requires a new sync before it shows again.
Have you noticed that some of your sites get disconnected?
Nothing has disconnected in the past few weeks. I should mention that I have closed the browser tab overnight, so I’m not sure if that has something to do with it?