Been trying to edit 4K video today from a Panasonic GH4 and Sony RX100 but it keeps crashing when editing and mostly during playback. It happens when the video files are in the camera roll and when streamed from Dropbox. I’m on iOS 12.0 on an iPad Pro 12.9”. Same thing with 1080p footage from the same cameras, but not as frequent.
Sorry for the problems you're encountering, Robin. We're aware of stability and performance issues with 4K media on iOS devices, especially when the sequence has 4K clips on multiple tracks. Titles and color filters tend to make matters worse.
Our top priority at the moment is to resolve these 4K issues as quickly as possible.