When importing H.264 MP4 source media into a sequence that has a different frame rate than the source footage, playback at full resolution slows to a halt. When switching to 1/2 res, the footage plays back fine. When setting the sequence to match the frame rate of the source, the timeline plays back fine even after setting the sequence back to a different frame rate. It seems to me timeline performance will only be acceptable when source media is imported into a sequence that matches the frame rate and played back before changing the frame rate back to another value. Source media used was 1080p30 NDF H.264 MP4, sequence set to 1080p60 on PrPro v22.0.0.44 beta. This is a new issue that did not occur in past betas.