This is Brushify pack I guess? I personally can’t figure out a way to set all grass meshes to movable.
My trick would be TSR + Use ‘Write during base pass’ for Velocity Pass (under rendering setting). Credit to: WPO issue in UE 5.0 on all materials, severe smear/dither - #10 by flankey
It is a hard fix but good news is that dev team is internally tracking this issue and let’s hope it gets fixed in next version.