When in doubt, call a Mitsubishi Diamond Contractor. They have the MNET TOOL (PAC-USB-001) diagnostic software that can map the network and identify exactly which byte of data is corrupt.
Do not just press the "Stop" button on the remote. Go to the electrical panel. Turn off the dedicated circuit breaker for the outdoor unit AND the indoor unit(s). You must kill power to the entire M-Net network. mitsubishi multi communication system reset
Flip the outdoor breaker first, then the indoor breaker (or vice versa; order rarely matters, but outdoor first is standard practice). When in doubt, call a Mitsubishi Diamond Contractor
While the power is off, open the indoor unit’s electrical cover (be safe). Look at the TB5 terminal block. Are the communication wires (usually red/black or white/black) tightly screwed down? Loose wires cause constant communication resets. Do not skip this. Go to the electrical panel