I have the same set up as you and ours moves a tad too! I think it’s down to the adapters!
We have it, no baby here yet but ours does move a bit. Not enough to think it isn’t on but it has a wiggle to it.
The cybex car seat on the mamas and papas flip xt2 does the same. I think its because its a different make car seat to base and on adaptors. We rarely put the car seat on the base as babies aren't supposed to be in car seats too long.
I have an ickle bubba stomp and mine does the same thing I thought it was down to going over different terrain! X
Yeah we have it and you just need to make sure it’s clipped in properly took us a couple of times to get it to feel more sturdy