What does "compose failure [UUID]" mean, and how do I fix it?

Question

I have a kext, and somehow os_log messages from this kext are being corrupted. The eventMessage becomes "compose failure [UUID]". The senderImageUUID and senderImagePath are set to some other unrelated kext. subsystem and category make it though though, which is how I can even identify these messages in the log.

It's doesn't have anything to do with what the kext is doing, because even if I put an os_log call and an early exit at the top of the init function, it still happens. So it must be down to something wrong with the project build settings.

What could be going on here?