I had to reinstall and wipe to get onto OTA-16 for some reason, but I'm not having the issue where calls / SMS aren't coming in after not restarting for 8 hours. It's been receiving and sending SMSs for about 18 hours. So I assume the issue is resolved. My 4G is still intermittent for some reason after updating the APN settings for my Ting with my credentials. I haven't tried reverting back down to 2G / 3G.

@triguy I'm sure you've seen the advice, but switching down to 2G / 3G instead of 2G / 3G / 4G helps. Also, doing a hard reset helps. Just shutting down doesn't always work for me, I often have to hold the power button for ~10 secs to restart the device and then networks come back online. I just do this daily at this point and am thinking of switching to Android until this frustrating bug gets resolved.