Disable MMS/Texting over WiFi

Here's another update on my recent experiences.

I have not had any problems with MMS for over two weeks.  I switched from Textra back to the stock Android messaging app with no problems.  I'm currently using the stock app.

I'm increasingly thinking that my problems with MMS were due to TMo congestion issues involving Android devices.  My wife never experienced any problems with her iPhone.  I experienced the problem with both Textra and the Android app.  I did get a message from Textra that there were "no MMS connections available" once when the problem occurred. I deleted all but a couple text messages from my phone to no avail, so the problem is not caused by lack of available space for messages on my phone.  I disabled wifi calling and still had the problem.  I forced the texting app to use mobile data and that had no effect -- I still had the problem.

I did enable the developer option "mobile data always active" a couple weeks ago, about the time I stopped experiencing the problem, but I can't be sure that really had an impact; I mention it for completeness.

I'm not sure when the next "congestion event" might happen, but I'll be alert for the next time I have a failure to send/receive MMS and report it in a new thread.