It usually is the other side as this is used less and tends to seize up more as a result.
It souinds as though it is not acheiving FULL TRAVEL on one of the lock mechanisms, so it thinks it should still be locked and sends a locked signal.
You need to take of the door panle etc and unseize the locks and or rods, the oe lock motor has not got suffecient pull in short space of time to overcome stuck bit most likely just some coppaslip on lock components will cure it, I would go for passenger side first.
tabetha