A bit OT, but my hotspot wasn't working either. I can't say which of these "fixed" it but here's what I did in case somebody would like to try. First I should mention that my SIM was from an AT&T branded LT1520 running 586.11. From the start I always had LTE, just no hotspot
1. Went into Field Test by opening the phone app, then dialing ##3282#
2. Clicked on Settings, then Band Locking
3. Unchecked a band, then saved & exit, then back into Band Locking to re-enable the band I just disabled (in my case LTE Band 1)
At this stage if I had waited a while it might have been enough but I'll never know because I was not overly patient at the time... then I dragged down the notification area and just started toggling everything related to wireless in random order numerous times - Cellular Data, Airplane mode, WiFi, Mobile Hotspot. Must have done a dozen combinations or so... then suddenly it started working. Sorry this is not very scientific or procedural but it was late and I was tired!
[Edit] I should add that while I set up the phone with a SIM card inserted I was a moron and accidentally put it into the SIM 2 slot. After initial setup I shut down the phone, moved to SIM 1, then proceeded to do all updates and configurations. For all I know this switchola was why I didn't have hotspot. Never hard reset the phone