Has the phone got wet at any stage @johnmully ?
Does this happen in your home area or everywhere ?
Your SIM card may also be degrading. As a process of elimination can you insert your sim card in another phone and another sim in yours please.
A Samsung service location or Samsung Experience Store would be able to run a diagnostic on it.
Daily Driver > Samsung Galaxy s²⁴ Ultra 512Gb ~ Titanium Black.The advice I offer is my own and does not represent Samsung’s position. I'm here to help. " This is the way. "