Skydemon and SoftRF (an open source EC device) are no longer fully compatible. The issue arises when SoftRF is operated in Pilotaware mode, and with Airconnect/FLARM protocol. After some experimenting it seems this is because SoftRF emits an IDtype parameter of ‘3’ in the $PFLAA sentence, and Skydemon rejects this with the dialogue “Unexpected GPS data”. Values 0/1/2 are accepted. I’m pretty sure SoftRF has not changed since December 2019 (when this worked OK).
2) Has this changed at the Skydemon end since Dec 2019?

Please make sure that the addresses being sent by SoftRF actually ARE ICAO addresses in that case. If they're not, there is a risk of address collisions with another aircraft. The Flarm protocol ONLY supports ICAO addresses and Flarm addresses.