Yes and no, they should be enforcing the ride height, the rear floor edges were rubbing on the track and presumably forming some sort of seal. The instability is causing the issues. One of the risks of introducing such a radical change.
Actually no yoiu have it the wrong way round.
Because the teams are trying to run as low as possible, to get the most out of the GE you get the porpoiseing, causing the issues.
Enforcing a ride height will loose a lot of the GE and have the cars loose a load of performance.
Teams will not be happy with that.
F1 and FIA introducing new rules, then enforcing a ride height that negates the new rules.