637114598 Legion Scarab of Eternal Conflict Soul Eater Immortality

Getting enough kills with legion scarab of eternal conflict appears to make monsters with soul eater take 100% less damage and render them unkillable while their soul eater buff is active. My understanding was that soul eater damage reduction(and DR in general) was capped at 90%. The Wiki does not list legion scarab of eternal conflict as a source of toughness but if it is, that could be the culprit, but I would have assumed the toughness from the scarab and the damage reduction from soul eater is multiplicative which should mean that I would still do some damage even if it isn't much. rounding error maybe??

Worth noting that there are wisps in this map which also give toughness but I experience this behaviour in virtually every map