Since upgrading to iOS 9.3, a number of Sprint users have run into issues staying connected to the carrier's LTE network. In a text message to customers today, MacRumors reports, Sprint said that it is aware of the issue and is work on a fix.
Your iPhone may be having data connection issues with the recent software update. We're working quickly to fix. We apologize for the inconvenience.
It's unclear how quickly the update may be pushed out, but affected Sprint users will hopefully have a respite from the LTE connection issues soon.
This follows the release of iOS 9.3.1 earlier today, which contained a fix for a web link issue that had been causing apps to crash.