OnePlus 3 - 2G (GSM) network not working - Selected network (o2 - cz) unavailable

I have a weird Issue with my brand new Oneplus 3. It's not connecting to 2G network, or it connects, but calling/data does not work. - when switching from 3G to 2G, it registers to network, even shows Edge sign, but calling and data is not working - when switching from 4G to 2G, it even does not connect It can be seen on a video I made - https://www.youtube.com/watch?v=CPlk8EEQsPE What I have tried: - 5 SIM cards from 3 different operators. All have the same problem, except T-Mobile, which was able to make a call once in +-10 attempts - flashing various versions of Oxygen OS (3.1.x, latest 3.2.7); flashing CyanogenMod latest; eflashed whole phone by Oneplus support using MSMDownloadTool - hard resets, *#*#4626#*#* menu settings etc... Nothing works. Could not find anywhere on the internet much more solutions to this. Guess it's hardware issue fro RMA? Anyone else encountered this issue?