Try downloading the "Change APN" app, and choose "Reset to default" from the menu.
Worked for me when everything except a factory reset would not.
I just ran into this with two phones moved to Tello. Update PRL and profile didn't fix it-- still only got 3g. I did the ##72786# thing and it fixed it.
The APN thing cropped up a few times this week over on the Twigby forum. Sometimes the ##72786# doesn't help and it needs the APNs fixing.
Where is the Twigby forum?
The APN fix is usually only required for Unlocked phones like the Nexus and Motorola devices.
The Nexus 5X all you have to do is dial ##data## > then tap APN in the menu > tap the 3 dots at the top right > tap reset to default> back out and carrier reset ##72786##
You really should be able to find a similar path on the Motos as well, but change APN does work as well.
It is always wise to perform a carrier reset ##72786# (##72786## most carrier agnostic Sprint compatible devices) whenever moving a device over to a new Sprint MVNO.
If you are activating a place holder and then swapping in a device to replace that place holder, I always run a carrier reset before and after the swap.