Removing STM32F4xxx based HMI from CANBUS puts the network in BUSHEAVY state
The bus load is supposed to reduce when you take away a node. If it doesn't, you either have only one active node and the others are silent. Resulting in acknowledge error. Or the nodes misbehave protocol wise.
Look on the bus (silently) and see what happens to the messages. If they increase, the unit that sends them does not understand CAN bus and you should contact the manufacturer.
CAN bus frames are not supposed to be sent back-to-back, there is supposed to be a minimum interval of 10-100 ms or longer depending on bus speed. Maximum bus load should not exceed 50% in all conditions, typically you want less than 30% before serious jitter is inserted.