Gracenote have indicated that they fixed the time-offset error on channel PosiTV that you reported here Live TV EPG - The update you’ve been waiting for - #1340 by pl4151
If there is a problem with other channels please provide details
Also compare on different Plex apps to see if any residual issue you have is just on the Plex for Mac app - compare with the plex clients that you have Plex for iOS and Plex for Apple TV
