The manual shows an external TS for shore/gen, then the charger/inverter then the CB panel. This suggests that any charger/inverter internal TS contact problem could effect all AC power including the heat pumps.
A number of different problems with the heat pumps or elsewhere could cause a contact issue. A power outage problem cause contact arcing as the power goes off and on. Including the inverter switching on/off to supply AC power to the panel.
While my chager/inverter is not a whole house type unit I never leave the inverter on which allows automatic AC switching. I also turn off all loads before connecting/disconnecting AC shore power. Both of these significantly reduce relay contact arcing.