I read a 200 amp main CB; 100 amp heat pump electric heat.
110/135 amps on main line side w/elec HP 'on' & main was buzzing/humming. One line side conductor 'warm/hot', & MCB was 'warm'. Also a 100 amp feeder to the HP w/2x60 amp CBs for the elements.
Bottom line IMHO sounds like an internal MCB issue, possibly a deteriorated termination on the 'warm/hot' line conductor.
Yes, the artic snap is overworking HVAC equipment,
