I don’t have problem with plex auto scan for my big gdrive library with the latest stable 1.4 with plex integration disabled. Changes are immediately detected on plex whether it’s local or in gdrive, and i usually do a lot of changes in a day : renaming tv shows files, adding subs, uploading 25 movies, 50 episodes, etc all typically happen in a day. With api polling works, all of this are instantly picked by plex regardless i change it via cache or via gdrive webui etc.
However as soon as i use plex integration then plex scanning seems slow or stalled in a plex library section that’s why i left plex integration disabled. For example, plex would instantly recognize changes of all 50 episodes I recently uploaded in the past hour but plex scans would never finish tv shows section thus the 25 movies i just uploaded is never picked up. So with plex integration enabled, in this case i would have to cancel the tv shows section scan, and then initiate scan in movies section.