Hey, I just recieved my new router today. The issue is fixed. I still don't understand what caused the issue in the old router, but thank you for suggesting this.
Have a great weekend,
sleight :)

In T153999#2109597, @Geez wrote:

Hello sleightush.
Would it be possible for you to try a different router from the one you are using currently? As some players have reported issues in the past that were tied to the routers they were using.
Regards,
Geez

Hey, just to clarify- i've tried playing with mobile hotspot connected to my computer using a USB cable and it seems that its working flawlessly. That confirms that the problem is with my internet, but I still have no clue on how to fix it.