After 6.0 FW upgrade I get absurd stats after training with Fenix 5 Plus, Zwift and Tacx Neo, e.g. 60000 W max power or w/kg FTP of 1125 W. The W numbers during training look OK, though.
Seems to be FW bug! never had this behaviour before...
Just spoke to Garmin support. Was advised this is a known issue and is set to be rectified with the new public update. Currently not available - no date offered but the beta is available at https://www8.garmin.com/support/download_details.jsp?id=14335 and from the comment above, this appears to have fixed the issue for some.
Funny that. I've been going back and forth with Garmin Support about this for 3 months.
I've now had to escalate to Fair Trading. Appalling behaviour from Garmin, who treat their customers with complete and utter contempt.