I’ve been encountering this quite a bit the last couple of weeks as well.
The latest site was running 5.7.3 and was showing “Automatic update is unavailable for this plugin” on the Plugins page. I went to Dashboard -> Updates and tried running the update there, which failed saying the package was not available. I refreshed the Updates page using the “Check Again” button, then went back to the main Plugins page and the notice was gone. I was able to successfully update at that point.
Will have to give it a try on the various other sites I’m working on to see if that works consistently.
