Model : C2600

Hardware Version : V1.1

Firmware Version : V1_150924

ISP : IZZI Mexico

Hi all,
I have an Archer C2600 hardware V1.1 with firmware V1_150924, purchased in Mexico, installed in the common/sitting area of a small school, max 20 users. Once, a student showed that her phone would not connect (newish, high end, HTC). Power cycle the router and the phone connected and stayed connected, at last for a while.

The latest firmware is C2600(US)_V1_160622, the notes say that it is made for the US and not downgradable. Should I upgrade anyway? Is there something that would make it incompatible with Mexico?

Thanks for advice and opinions!