It looks like Power Cogs's knockback debuff has a hardocoded max timer in its codes, which prevents it from ever lasting longer than the hardcoded value.

The debuff itself is affected by status resistance, lasting longer/shorter.

When you have positive status resistance, the buff lasts shorter, so the knockback is horter and the damage/mana burn happen sooner.

When you have negative status resistance, the max timer prevents the knockback from lasting longer.

Very simple to fix. Remove the timer completely. The effects already happen when the debuff is destroyed (as proven by positive status resistance), so there is no need to have a timer that destroys it after x seconds.