When something hits the player, it needs to know the amount of momentum to apply on the local mobj, not the absolute momentum on server side (which is by definition obsolete for the client's movement).
Now collisions and other impulses are sent as momentum deltas in a GPT_MOBJ_IMPULSE instead of using FIXMOM.
FIXMOM doesn't work for impulses
When something hits the player, it needs to know the
amount of momentum to apply on the local mobj, not
the absolute momentum on server side (which is by
definition obsolete for the client's movement).
Now collisions and other impulses are sent as momentum
deltas in a GPT_MOBJ_IMPULSE instead of using FIXMOM.