Engine overheating/radiator fan issue

[N20MY]

Hi bros. Have a problem with my F30 328i and would like to seek some input from you guys who might have experienced it:

1. Car entered limp mode and air no aircond
2. Then overheat warning came up
3. Scan shows radiator fan kaput and a weak battery. Visual inspection fan really wasn't working. Changed fan, fan relay together with battery.
4. Radiator fan still not working even after replacement
5. Mechanic followed BMW recommended troubleshooting plan: cable, relay, voltage, etc etc still unable to find the root cause.
6. Miraculously, fan came back on without any additional rectification. Was okay for 2 days straight of testing
7. Then it went dead again
8. Since then the fan goes on an intermittent on/off craze

Some say its DME (which I really hope it isnt) and some say its some other sensors, etc.
Any of you bros have any clue/experienced this issue? Was on JB4 before so not sure if this might have caused it.