iPhone 8+ keeps losing ability to make calls

For the second time in about 5 months, my iPhone 8+ keeps losing the connection required to make calls and send or receive texts. This typically occurs while it sits unused for a period of time such as overnight, but it can happen if I don't use the phone for an hour or so. When it happened before, I took it first to my carrier and they updated, changed, deleted some phone properties and it worked for a couple of days before it started having the same problem. I took it to Apple and they eventually had me do a partial reset (I didn't completely have to go back to the factory settings) but I did lose a lot of information that I have had to re-enter. The person at the store told me if that didn't work I would have to bring the phone back in and they would have to go to factory settings and reinstall things one-by-one to figure out the problem. Obviously, I would like to avoid that if there is anyway possible, especially since I am nervous to do it by myself and Apple stores are closed. Has anyone else had this problem and, if so, how did you fix it? Thank you.