I just did an FTP test. 20 minute - short protocol.
It told me that I did 329w for 20 min (that appears correct) and that my new FTP was 313w (also correct). When I went double-checked the update, it had updated to 318w.
Assuming that I had too much sweat in my eyes I confirmed with my feed to trainingpeaks - and sure enough - 329w for 20min and an ftp of 313.
I point this out because I see A LOT of complaining about bad cat enf in the zwift subreddit and this COULD be part of the issue.