@magikmark
Thanks very much for the tailored advice. 👍
The fq_codel error logs are pulled from /var/log/system.log so they also show in the GUI under Status/System Logs/System/General.
For whatever reason the errors promptly ceased after an unrelated update & reboot, so I have not had a chance to apply and monitor the suggested values. The 'observer effect' no doubt.
☕️