xjokux - i had a different car that did similar thing, all doors would open except one or one would go intermittent / buzz crazy.
basically after talking to my installer who did the job nearly 5yrs prior would had come across a situation on that platform before with a third party immobiliser alarm suggested that it can be attributed to that during either winter the battery labours more and or you use headlights in darker months OR during summer using air-conditioning the starter motor more so battery drains on short trips and the alternator doesn't charge battery up enough but it may still start the car. my solution was regulator replacement with new bushes and de-sulphating charger on battery as the actuator tested fine in isolation.
try elimination-
clean battery terminals and ensure earth is secured and not corroded
check all fuses in engine bay and ones in drivers foot-well, lightly apply conductive grease when replacing
trigger test the actuator in isolation to make sure the motor can freely move the arm component, WD40 or grease if required, make sure the ground is 100% especially if it is third party mongoose etc if not mitsubishi OEM
check the tension of belt on alternator to make sure its not too loose/tight & run multimeter over battery terminals while car is running is 14V+
buy a bosch regulator with new bushes already attached & replace (repeat voltage test)
put your battery on a desulphating charger like an optimate (or ctek) that tests the battery
if it still not fixed next step would be to get your alternator rewound/refurbished and or consult auto electrician to track down a potential parasitic draw
ps. not sure if you still have the motorcycle in your signature as i dont recognise your handle from brissyriders but an optimate works amazing with them too, well worth the investment.
