Drawing hot water in wash machine trips tankless heater breaker

[ddproperty]

Issue started with new LG washing machine

Can run 3 sinks and a shower at full hot with no issue but when washer draws hot it trips the first breaker on tankless water heater.

Heater is two double pole 40 amp breaker. Heater operates "as normal" even after first element is tripped.

Thanks in advance