Prior to the 9.0.1 pre-patch, I had installed a couple of addons via the Twitch app and changed their install preference to alpha instead of release, notably Ace3 and OverAchiever, and a couple of others. Since patch day, these addons have been updated and flagged as release builds by their authors. However, both the Twitch app and Overwolf Curseforge app attempt to update these in endless installation loops, going from alpha to release to alpha to release, etc, and so on.
The workaround is to delete these addons and reinstall them, because changing their installation preference in the Twitch or OW apps (right-click, install preferences) does not stick. Naturally, this is not a good solution, as it also deletes any settings for those addons in the game.
As far as I can tell, this bug only applies to addons that are/were installed as alpha versions, although beta might be affected. The bug does not happen with release versions.