Sorry for the delay in posting this, but Apple pushed out iOS 14.2.1 a few days ago that fixes a bug where MMS text messages were bot being received in some cases. I know my wife was having these issues ever since upgrading to the iPhone 12.
This may have fixed the issue but if you are missing a text message, how do you know unless someone tells you later on.
This update also fixes a bug that caused the lock screen of the iPhone 12 mini to become unresponsive.
Here are the direct download links for iOS 14.2.1: