You’re saying generic IO errors, but I’ve found rclone logs to be pretty specific when set to debug. At the very least what part of process do the errors start happening? Good place to start. Haven’t used gdrive in a long time, though as I recall they used to have rate-limiting which could be a factor as well.

Another question is if the problem is moving after file completion, why stick to rclone if you’re running into issues? Moving deluge completes to a local fs to check for errors in that process, and then either manual or a cron/timer/script with something like rsync for the final move would work for troubleshooting. At some point you’re going to run into an error more detailed than “IO error.”