For the error logging issue, there’s not a way around it as it’s being caught by line 48 in Houdini.py:
self.AddStdoutHandlerCallback( "(Error: .*)" ).HandleCallback += self.HandleStdoutError which goes off on any line starting with “Error:”. I suppose a person could ignore lines that have ‘Caught exception’ in them since we can assume the next line will have the helpful error text. I’ve made a feature request with your info.
For the plugin sandboxing error, it looks very similar to the one shown here, and I’m hoping I’ve got it fixed with that updated PDG submitter file.