Prores bug on OSX using ExFat exernal drives
I found a bug on at least High Sierra and Mojave in all versions of Premiere Pro 13.x (2019), which happens when trying to edit prores files off an external hard drive. If the hard drive is formatted as ExFat, your timeline playback grinds virtually to a halt, and editing is impossible. As soon as the same project is copied to a drive formatted to MacOS Journalled, it plays normally.
Thank you for the report. This issue has now been fixed in the 2019.1 release.