LG G3 successfully installed CyanogenMod 12, but having SIM issues.

I successfully installed CyanogenMod 12 on my LG LS990, but I'm having some problems involving the SIM card. My carrier is Cricket (or AT&T), and I am able to send and receive calls and text messages, as well as download and browse the internet. The speeds are very fast.

However, it gets wonky most of the time. On the notification menu for my G3 as well as the phone setting, it is still listed as Sprint. It will also turn off randomly and show an "R" at the top and will glitch out. On several occasions, a pop-up will show up and say something like "com.phone.android has stopped working" and the bars at the top will disappear all together. This seems to happen when I turn the display off or put it to sleep

On the mobile data settings,I have put data roaming on, LTE, CDMA roaming to automatic and "NV". I am not sure what most of these settings mean, but on the access points menu " cricket" is checked. I cannot change the NV setting to SIM.

I receive notifications from Cricket. Texting and Calling works completely fine. I'm wondering why it stops working for a while when I put the phone to sleep or why everything is listed as Spring when it isn't. Thanks.