Not sure what this error means

[BlakeB5061]

I am currently running this on Unraid in a docker container. I set up the temp folder as required and the subfolder structure was populated correctly. I've put folders containing MP3s in the "recentlyadded" folder and it appears to be combining into M4B files as intended. The only issue I'm having is that I keep getting the same error message every time if finishes a folder, but the output files seem to be OK. This may be an error that is irrelevant, but I'd appreciate some input so that I can be sure. Thank you.