Motopacing is a big problem but it is there for basically every time a solo rider attacks. When a solo rider attacks, the motor will always go behind/next to him while the motor of the chasing group will always be in front of the group. So this problem wasn't there just for Van der Poel yesterday, it's also present every time one rider attacks. The camera wants to have a clear view of the group and the group dynamics, so filming the front of the chasing group with riders who are taking turns is more interesting than filming the buts of the riders in the back, i presume, when you can't see who's doing the work in the front of the group. For a solo rider there is only 1 guy to film so it doesn't matter that much and while filming from the back, they get a better view of the roads.
This was also quite apparent in LBL. When Evenepoel and Pidcock were riding away from Skjelmose and Ciccone, the motorcamera was in front. The moment Evenepoel dropped Pidcock, the motor went behind. While the chasing groups are usually alwasy filmed from the front, creating motopacing.