This fixed mine too. Deleted the 3 files named “tv.plex.providers.epg.onconnect*” then restarted plex server. The EPG downoload is still slow, (about 10% in 20 minutes) but at least it’s counting up, and not staying at 0%.
If it helps the devs; the hard drive I store my plex media player cache folder on has been failing for a while, and was recently backed up, replaced and restored.
So, the failing drive, and the replaced HD may have caused the issue. Just a data point to consider.
