Slow Logging when using Xiaomi

Hello.

I recently got a new smartphone, Xiaomi Redmi Note 4, and when I try to log in Pokemon GO, it usually, or like always stucks at the loading screen. Usually "Sign Out" button appears in the right corner of the screen and then Retry button appears, so I retry and after a moment it logs in or fails again. The problem is that logging in is very slow or it sometimes doesn't log in at all. I am using mobile data, 4G. Background data is turned ON for Google Play Store and Pokemon Go. Other than that, seems like internet is working well. It's just the logging part, but it's annoying.

Reason why this bothers me is because when I use my old smartphone, Samsung Galaxy S3 LTE and the same SIM-card, and of course same ISP, I HAVE NO problems with logging in, but game runs worse than on Xiaomi, a lot. So yeah, on S3 LTE, logging isn't slow, and I can't see "Sign Out" button in any point.
note: S3 PoGo is from apkmirror, Note 4 PoGo is from Google Play. And Speedtest.net proves that I can reach 50mb at the best.

Thank you, I hope I can solve this someday.