iPhone XS that was being used now shows "No Sim Card" warning

My wife's iPhone XS has been in use for over a year. Everything has been fine until just now.. She is showing a warning about the SIM card not being installed. The phone resides in a case and never gets removed. I took it out of the case and removed the SIM card and reinstalled it but the message remained. After fiddling with it, messaging seems to be working again. My own phone is an X and we are generally in the same places at the same times and I had no problems. The signal strength indicator to the left gf the wifi symbol was showing dots when the warning was up but now is showing normally.