iMessages displaying as “Not Delivered” since iOS 12.3.1 upgrade (iPhone X)

All my iMessages show as not delivered since upgrading to 12.3.1, but they DO send. I’ve also received some messages that have disappeared from a conversation later, and some messages that I’ve sent in the past have reappeared as my most recent sent message. So far I’ve tried turning the phone off and restarting the app. Didn’t see any other messages on the forum about this issue as associated with 12.3.1.