Can you tell me more about the 4K footage, which codec were you recording with, frame rate, Mbytes/second etc?
Hi Androu - once it had been on the timeline a while, strangely it sorted itself out and I could add as many transitions and effects as I liked and it would play back fine.
Linked to this though, I was editing something yesterday where I muted some of the clips in the timeline. However, when I played back the preview - some of the clips hadn’t retained the audio settings so that I kept having to revisit and correct them. Sometimes just muting and unmuting was enough but it wouldn’t retain this info. I had to make sure that this was the last thing I checked before exporting the final video. (It was a mixture of iPhone 6S and GoPro footage).
Are you aware of this bug?