According to one reddit user in California, he's having issues when his iPhone attempts to connect to a specific LTE band. Affected users are frustrated with the connectivity problems, with some reporting an inability to receive any messages or updates when not on Wi-Fi. Most users seeing problems appear to be using Apple's latest devices.
I'm having data issues as well on my 6s Plus in the LA/OC market. Over the past three days I've been troubleshooting on my 80 mile round trip commute via Field Test and Speedtest. I've figured out that data transfer is broken when connected to Clear B41. No problems on Sprint B41, B25 or EVDO. I've created a ticket with Sprint Care, and supposedly they have notified their network team. I'm awaiting a response.As of this afternoon, Sprint has begun sending out text messages to its subscriber base, acknowledging the data connection problem. Sprint says that it is aware of the issue and "working quickly" on a fix.
I've talked to Apple as well, they did a diagnostic test that came up normal...of course it did, because I was not connected to Clear B41 at the time. At this point, the only course of action is to either disable LTE or revert back to 9.2.1 before Apple stops signing it. I'm not sure if this has to do with the WiMAX shutdown in my market, but I have noticed that the TAC went from 9xxx to 3xxxx after the shutdown. I've restored three times via iTunes to no avail.
Apple this morning released an iOS 9.3.1 update with a fix for an unrelated web linking bug, and while it's not clear if the new update fixes the Sprint issue, it's unlikely as Sprint's text messages were sent out after the update was released.
Update 4/1: According to Sprint, the data connection issues affecting users were resolved this morning.