I had this exact issue about 2 weeks back here in Houston, it only happened in a certain area and turning on/off airplane mode fixed it over the short term.
I switched to the Tmobile BYOD sim since Im sure Houston will have PCS 3G here soon. I would recommend against any MVNO ATT sim, it seems that ATT wants people on their postpaid plans and if they aren't messing with the MVNO APN on purpose its extremely obvious that it's below a low priority to fix it when issues occur.
“A democracy will continue to exist up until the time that voters discover
that they can vote themselves generous gifts from the public treasury.
From that moment on, the majority always votes for the candidates
who promise the most benefits from the public treasury,
with the result that every democracy will finally collapse
due to loose fiscal policy, which is always followed by a dictatorship”