We experienced a bug that produced the same error message. In our case, it seemed like the issue was happening after using the copy method to create an immutable AVComposition from a mutable AVMutableComposition, and then letting the mutable version be deallocated while still using the immutable copy. We found a workaround by keeping hold of a reference to the mutable copy so it wasn't deallocted while using the AVComposition, so it's possible a similar solution will work for other cases of this bug. Good luck!
ltctk
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