Why my phone sometimes doing no sim or no service?

I have done my 5s screen replacement recently. After replacement, everything works just fine. After a few days, it was starting to do no service and then no sim installed. Sometimes, it became normal again after a hard reset. Sometimes, it needed reboot. I tried putting another sim card. It showed the same error. When it became normal, after a few hours it started doing no service and no sim card insalled again. I have to do a hard reset every time it becomes. Sometimes, even hard reset and reboot cannot solve the error. I have to wait a few hours to become normal again. Please help me!