After Some Time my Serial Port Stops Refreshing

I have noticed something strange. Everytime the hours and minutes reach a full number the system time stops refreshing. For example: 17:00, 20:00, 02:00, 03:00, 20:00 and so on... That's what's going on. IIt stays this way from 00 until 10. After that,i rewrite the new time to turn on and off and it starts working again. Does anyone have an idea about this? Also, huge thanks for the time and attention to help me.