When trying to debug an issue looking at the PyXLL log file is usually the first step.
By default, PyXLL logs to a "logs" folder in the same location as the pyxll.xll file.
The location of the logs can be configured in your pyxll.cfg file. Check in that file for the LOG section. There you will find the location of the logs folder and the filename of the log file.
If you are using the exampe ribbon, you can open the log file directly from Excel via the PyXLL Examples tab. Alternatively, if you go to Add-Ins -> PyXLL -> About PyXLL... the about screen has a link to open the log file.