It’s not a bug – it’s an undocumented feature.
The Alpe du Zwift segment in Zwift Power gives an average power over this segment that does not correspond to the Zwift one….

I had a best time of 58:08, with a average power on Zwift of 261, while it was on Zwift Power 58:08, with an average power of 217.
Did a 54:48 on Zwift today, with an 273 average power. Zwift Power gives an average of 235 (same time).

No clue how this might happen.
I see the same thing for me. Says 207W avg, but my strava says 213W avg for the segment. I did notice that my average power for the whole race was about 207W.
If I recall correctly this segment has a known bug where Zwift reports inaccurate data to ZP.