No service on band 12?

I have' no service no signal' at all at one of our office locations, indoors or out.
The mint mobile coverage map shows 600 and 700 dark green 4g LTE at this specific location.
The tmobile map shows'good' coverage.
My moto g4 has the 700 4g LTE band 12.
One of my co workers who is on tmobile does have service which works well at this location.
My phone/ data/mms works well at other locations.
I am using the mint apn settings.
Any ideas?
Thanks in advance.

Perhaps rebooting the phone might help. If you can check the coworker's apn settings and maybe even try them on your phone, then let's see. I suspect your phone might revert to the Mint supplied apn settings if they differ from your coworker's T Mobile apn settings.

Just quick thoughts:

als-- you say the map shows good 600 and 700mhz coverage.
Your Moto G4 likely doesn't have band 71 (600mhz), or band 66. .
Are you sure that your co-worker is operating on band 12/700mhz? If not, can you ask what phone he/she is using, and confirm whether it has band 66 or 71? (I think this would be an unusual geographical location, but possible.....and not many phones have these bands yet.)

Might also be worth confirming that you have VoLTE enabled. I can't remember the details, but I seem to recall some strange results if a phone has band 12, but without VoLTE enabled. If it's enabled, try disabling it.

use one of the other tmo apns to see if that helps.

Any chance your co-worker has T-Mobile Postpaid or Prepaid service, instead of a T-Mo MVNO? If so, perhaps you're in a roaming area not available on MVNOs. I have little experience with T-Mo coverage mapping, but I've read it can be somewhat optimistic. (A situation typical for all carriers......)