I'm not sure how this would or could be fixed but the lag from trample is assessed after a set number of hits so the person can wimpy and suffer their lag at that point and you're always more lagged than them.

Reproduced every time I tried when someone was (RIGID) and low health and tried to trample to keep them in combat.

If I understand your post correctly you're saying people sometimes wimpy out of trample.

Correct.

You can wimpy out of almost every damage type in the game with few exceptions.