I've had a Nokia 5 for some time now and it has been running Oreo 8.1 just fine as well.  Starting to have a few issues sending text messages to isolated users.

Comes back with an error 38.  Essentially once this happens I cannot reply to messages or initiate messages to select individuals.  (currently 3 people in my contacts list). 

Had a suggestion it might be a flakey SIM card.  Looking for confirmation or insite or some trouble shooting steps please.

Thanks