libCEC do not like it when the CEC connection got stopped like by switching “hard” the HDMI-CEC line.
Also 99% of CEC issues are related if this connection schema is used: device -> AVR -> TV
Also Onkyo is known about having a bad/special CEC implementation.
Also Panasonic is known about having a bad/special CEC implementation.
For Panasonic you can try to change the libCEC version:
Maybe it helps or it make thing more worse. Last step is to create a issue here: