Default [Q] my D801 semi-randomly freezes and reboots

It seems to occur most often when I'm using Google play music. I think I see the sync icon go as well. But I haven't been able to reliably recreate the problem. I'm on a slimmed down stock ROM. Before, I was on rooted stock with lots of G2 exposed features on. Is there a good way to diagnose the cause? Should I revert to stock entirely and try to get it replaced?

Also, sometimes my data runs excruciatingly slowly, even though it says full LTE signal, and it's a site that is quite reliable and definitely not the problem.

I also have been receiving texts late (sometimes 24 hours later) recently. I have experienced similar things before on different phones, but maybe there's an actual software solution for that.

Thanks for any help