I have a few of the EC25-V, certainly seen them working in a wAPacR and long ago a RB922. But no NetMetal. What issue are you seeing? Normally the key thing with the EC25-xx is to get them to MBIM mode for ROS 7 & for EC25-AFX, another thread suggest you need firmware i>EC25AFXGAR07A03M1G – see
http://forum.mikrotik.com/t/how-to-send-at-commands-to-ec25-lte-modem-in-ltap-mini/131542/1
I offer that we’ve actually moved on the Telit 960. Re FirstNet/Band 14, I’d see the Telit actually use B14 from the Mikrotik as 2nd DL CA for non-FirstNet customers. I’d thought it was a bug, but apparently AT&T allows it if FirstNet isn’t congested.
Anyway I’d bet your issue with the EC25-AFX is the firmware, so I’d check that first.