I'm working with 4K, 60FPS MOV files from the Panasonic GH5. When I play these files in QuickTime Player 10.4, the playback is smooth, and I can jog around the video file with ease. No issues.
But playing back the same files in the source monitor in Premiere Pro 2017.1.2, the video skips frames galore and is basically impossible to playback. Even at 1/4 resolution, though it plays back OK, it is hard to scrub through.