Lately I often get blocked by a slower rider. It happens in different occasions. For example when I am riding in a group and we overtake a rider, the other riders of the group overtake this rider easily but I get stucked behind this slower rider and lose contact to the group. It also happens at the Alpe du Zwift when I close a gap with some speed difference, but when I get close behind this rider my speed suddenly drops and only with extra power I will overtake this rider.
It is getting quite annoying since it ruins races which I do. I am getting dropped from a group with no reason.