eu rom bugs

I just downgraded my phone from a global rom with the android 11 version but it contains so many bugs that I chose to downgrade it to this xiaomi,eu rom from this forum. I hear that this one might contain some of the bugs that the global rom have so I am making sure to know the difference so I...

I bought a China version of K30 5G Racing and unlocked bootloader and everything then flashed to eu rom, everything works pretty well EXCEPT the mobile data connection. When I am still in CN version, I can use 4g anytime and still get good high speed connection even when I'm inside the house...