Sometimes the solder connections on the board go bad. You might try to resolder all connections on the board. Also, clean the contacts where it plugs in. The fact that it works sometimes indicates a bad connection or an overheating component on the board. I'd try the resoldering solution. Use a small soldering iron.
Clean where board plugs in first. If that does not work, then I'd do the resoldering.
I once had a Mercedes HVAC board that would suddenly turn the heat on in the summertime. It turned out to be an overheating transistor that would break down when it reached a certain temperature. I found it by spraying refrigerant on it while holding the board in my hand hooked up by a bunch of wires instead of being plugged in. When sprayed with refrigerant, the heat would turn off and AC would start. As it heated up, the heat would come back on. Replaced transistors.
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