Optimize never works: undefined failed items

Hi!

When I try to optimize media, it always immediately fails. It appears in the Optimized Versions tab as “undefined failed item”. Curiously, if I try to Optimize the same thing again, it then reports that “The media version already exists”, although it does not. Sync with transcoding works–I can use my iPad to get a “Low” quality synced copy and it will transcode and then eventually transfer.

When I manually inspect the filesystem where Plex should be storing the optimized versions, I do not see any optimized versions, including media for which Plex shows “The media version already exists” error.

I’ve glanced through the logs and must be missing something, because I don’t see a relevant error message. In the attached logs, I tried to Optimize “Mad Max: Fury Road” just moments before downloading the logs.

I’m running Plex Media Server 3.9.1 in a jail on a FreeNAS machine. Other functions of Plex seem to work correctly.

Can someone please point out the relevant logs to me? Even better, can someone tell me what I’m doing wrong?

Thanks!