For me, almost every time Channels failed to re-auth a Discovery Channel when its token had expired (expires every 7-8 days) was when it was trying to record the channel. I was then able to get the channel re-authed by playing the channel Live in the web UI player.
If you're still periodically forcing a rescan of all channels, that wouldn't help.
Appears there's a difference in the auth flows for rescanning, recording and trying to play Live.