Usually the SM-G900V comes with Verizon (USA) > CSC = VZW.Hi again,
I have a mint condition unlocked Galaxy S5 SM-G900V running Android 6.0.1 I bought from ebay. The firmware is G900VVRU2DPG2 and *#1234# shows the CSC is G900VVRU2DPG2. The About Phone software area shows United Arab Emerates and booting into recovery shows the CSC is set to XSG (United Arab Emerates unlocked). I live in USA and the phone does not connect to all mobile networks like me old S5 did. I think the problem is the lower level CSC is set to XSG instead of XAA. Everything I've tried to change the CSC to XAA has failed. Does anybody know a sure way to get my CSC changed to XAA on this phone?
As the G900VVRU2DPG2 is not the latest firmware version, you can try to flash latest version G900VVRU2DQL1.
You can download latest stock firmware on different dowload sites - just search for "stock firmware SM-G900V". There you will also find guides how to flash.
Or just have a look here: https://forum.xda-developers.com/t/...sung-galaxy-s5-sm-g900v-kltevzw-odin.3757416/
About changing CSC ... I just know a methode which needs root and doing a factory reset. That is not a "sure way" IMO.
I hope that flashing latest stock firmware will fix your mobile network issue.