Sprint has now found the issue and solved it with an easy to install update. They have solved another issue many were having where 4G hotspot connections would periodically disconnect while on a call. The update is rolling out today via an OTA. As always with any OTA it might take a little bit of time for all devices to receive it. Be on the look out for that wonderful ‘update available’ screen, but be sure your device has over 50% battery and you have about 10 minuted to complete the download and update.
Source: Sprint