Hi, my name is***** your mechanic automotive expert, and I will be happy to assist you today. In some cases, I may need more information to assist better. I apologize for any delay.
Dear customer, there are several factors that can affect this problem with the central locking system. Your Kia works with a module known as the central locking module, this module is the one that receives the signal from the key fob and encodes it to activate the signals of the selenoids and allow the opening of the vehicle, it may be presenting problems in the module because it is taking time receiving the signal, in these cases the ideal is to start verifying with a diagnostic tool with Kia software and verify you do not have problems or error codes referring to the central locking system, if all this is correct, it is good to do a check to the fuses and relays to rule out
It would be good to try with the replacement key, because many times the key fobs are constantly subjected to blows, these blows cause the internal chip to be damaged over time, the problem may be the fob chip and it must be replaced, if you do not have an spare fob. These fobs are not expensive and you could try replacing them, if with the replacement key the problem persists, the fault will most likely be in the module and it will have to be replaced because the key fobs are correct and surely the module has problems receiving the signal.
My goal is to give you the best advice i can based on your description, I hope to be helpful, if you have any doubt please do not hesitate in reply back.
Kind regards, Sebastian.