QT MOVs that are ProRes 4444 1080p have poor performance in the viewer and player. Very sluggish when scrubbing and playing. Playback is OK in an external player. Seems OK for clips that are ProRes HQ or less. Could this be an issue because of the embedded alpha channel in the file (even for camera files)?
Thanks for the report, the issue will be solved in the upcoming beta 5 as part of the ticket you reported, this is just in case others have the same problem.
Best wishes, Thomas.