This is identical to what I see. Yesterday, riding downhill from ADZ, I was experimenting with supertuck (which worked). Upon reviewing my Zwift logs on Strava, there were a couple of 2000W surges around the time.
Flux 2 also seems to lose cadence/speed tracking if I stop pedaling (this is essentially the second unit I use. My Flux 2 internals were completely replaced due to noise. The previous one behaved similarly)
This is not a Zwift issue. I’ve been logging this ride with my FR935, independent of Zwift. Sure enough, the same 2000W spikes appear there as well. I will soon be contacting Tacx support, and will update here as appropriate.
Update: Moved from ANT+ to BT; made sure no nearby 2.4GHz WiFi source was active. End of ride: 0 cadence, 2000W.
Still unable to repo unless Zwift is present…
Update 2: Another ride, this time using Tacx training app only (also tracked by ANT+ watch.) Two abnormal high-power occurrences: one 850W BT reported (accompanied by cadence spike), another 1788W (with 0 cadence) ANT+ reported on another location/ride.
Based on the above, I would say this is not a Zwift issue.
Update 3: Another day. Another ride. Tacx app only. Again, high power spikes on both ANT+ and BT.