Hard reset the device, do not install backup, and then try to send/receive MMS.
I tried this twice and still won't work. 😭
No, a hard reset is when you erase everything on the phone by dialing ##RTN# on the dial pad or going into settings and erase all content.
Is the hard reset when you push volume down & power button for 10 seconds?
Did you get the update OTA from Sprint? I ask because that behavior is not from the update, you have an app adding that on. I had that problem quite awhile ago and it turned out to be some app I had installed. There are apps you can find in the Play store that will scan your phone for apps that embed advertising so you find and delete the one causing the problem if you can't figure out on your own which app is causing the problem.
I got the notification on my phone that an update was available. I hit update. Do you by any chance know the name of the app that can help find which app installed is doing this
If I remember right the app I used was called something like add-ons detector. But that was awhile ago so the app might not even exist anymore as mobile security apps look for malware without being specific to just adware. If you have a mobile security app you can try running a scan with that first.
Sprint uses Lookout Mobile security so there's a good chance you already have that installed if you haven't taken steps to get rid of it.