It had seemed when I first got the device up and running that everything was fine with MMS (that was using 4.4.2, Sense 6.0), but either after a certain number of messages, or while in certain areas I would have to turn off WiFi to be able to send MMS.
That's why I tried downgrading to 4.3 with the alternate version of Android Revolution HD (essentially a tweaked version of the stock HTC ROM). What I find odd about the two version of that ROM (30.6 vs. 71.1) is that the installer for one includes an model selection screen and the other treats them all alike. 30.6 allows me to choose between International, ATT/Developer, Sprint, T-Mobile, etc.
Initially I chose ATT/Dev as that's the hardware model of my HTC One and wasn't keen to deal with a soft-brick. As stated in my first post, this seemed promising initially but shortly after ran into the same bug. I flashed one more time and tried using the 'T-Mobile' model selection during install. This has proven the most reliable method for me thus far. I suppose it would have to do with the radio being flashed between versions? It's curious to me that a similar option is not included in the other ROM version -- something I wanted to address in that ROM's development thread, but am prohibited from doing currently due to my post count.
Anyhow, 4.3 with Sense 5.5 seems to finally be working for now. Android 4.4.2 and Sense 6.0 did have some some aesthetic differences that I preferred, in addition to seeming marginally faster. I'll deal with an older version of the OS though if it means my phone functions properly.
Thank you both for your replies.
One thing that may be worth mentioning is that I've yet to enable Group MMS in my messenger settings this go-around. I suspect that its coincidental, but I'm reluctant to see what happens if I do enable it.
Maybe I'll try again with 4.4.2 in the future, but all this flashing, re-flashing, and settings tweaking becomes pretty tedious. In relation to that point: Does anyone have any experience with the built in HTC/Google app backup/sync. For some reason I've never really trusted any all-in-one solutions to be reliable, especially between ROMs or Android versions. Perhaps I should trust them more?