iOS Blackmagic Cam interrupted/lost numerous recordings

Hi, for the first time I used BM Cam iOS instead of the built-in camera app, for manual exposure. I ended up with 2 sub-4-second videos and 1 video interrupted after 17 mins. The remaining videos went for an hour each with no issues. I had 100GB free space and had recently deleted 60-GB files and verified free space was reclaimed, so I doubt fragmentation was an issue.

I lost really valuable footage. Have others had the same issue? How do you record on iPhone then?