Cannot connect to a data connection on Sprint HTC One M8

Firstly, I am running CyanogenMod 12.1 on my HTC One M8 , but this is an issue I also experienced running stock Android (e.g. Lollipop). The issue I am experiencing is that my device appears to be unable to reconnect or "get back" on the Sprint data network. For example, yesterday, I was in NYC (obviously somewhere that should and is covered), but I was unable to get a data connection anywhere in the city. I was only able to send SMS (*not* send/receive MMS) and make voice calls. In the past, when I had this issue on Sprint, being the helpful individuals they are, they told me to restore my phone and reinstall Android. I did that, which helped for a while, but it wasn't long before I ran into the same issue on stock Android. After a while, the issue seemed to "resolve" itself magically. I never found out why or how. More recently, I rooted my phone and installed CyanogenMod 12.1 on my M8, and I am running into the exact same issue I had before. Ideally, I don't want to have to restore my phone again, because not only do I not think this is the "fix-all", but it seemed like Sprint's lazy answer for not wanting to actually troubleshoot my device. This is becoming increasingly apparent when I travel as I am unable to get GPS directions, send MMS messages, or do anything over data like normal when I'm off of a WiFi network. Despite having "bars" on my screen, CM will display a small "!" over my data icon, which I assume is an indicator that it is unable to connect to the mobile network in some way. Is there anything I can do to better troubleshoot my mobile data connection?