Recently bought a new phone MX4 pro.. Then change the new simcard with "U" which support LTE.

I realise that the signal drop only happen when i am in the office. No server network, cannot call out/in. There is one time it happened, i walk out from office with the phone to open space, automatically it connect and have strong line.

I check with colleague using Digi has strong line in office.

I flash the ROM with latest version, still same. Report to Digi and restart for me still same. Change SIM card with group 40 still same.
Don't know is Digi problem or the hardware problem.
Any Digi user also encounter this scenario totally cannot call and no network with other phone especially got 4g ?