I've looked at the error message and the log; our code was calling the zip library's zipOpen() function to create a new zip file (within your OmniFocus.ofocus), but this was failing for some reason which unfortunately wasn't captured in the log.
Is it possible that your hard disk was full? Seems unlikely that you would have missed that as a reason, since the operating system probably have prompted you with some other alerts about that. But it's worth checking.
You mention that the POSIX permissions were set to 0755, but is there any chance the Access Control List or ownership on the file could have been set to the wrong thing? (This is pretty rare: we usually only see this right after someone migrates their account from another computer.)
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