Noticed something similar on TdZ Stage 5. My group was chugging along at 2.3w/kg catching a small group ahead. I noticed a rider in the group ahead had a power drop or took a break cause they went from 2.0w/kg down to 0.4w/kg. Right as I get to them their power goes back to 2.0w/kg but their speed is slow because of the decline in power before. Zwift sticky drafts me to then and i instantly lost 10km/h on my speed even though my power was constant.
Rightly pissed me off and a few choice words may have been yelled towards Zwift as I lost my group and had to put in a hard effort to catch back up. To make it better this was about 8km from the finish of the stage and I burned too many matches getting back to the group I dropped from but was with the whole ride I didn’t have much left for the after party climb.
The only solace I took from it is that it was a ride and not an official race, but still irked it cost me probably 20 spots in the final.