Doggy, VPN that you are using does not confirm that it's not a problem with ISP, it could as well point to the ISP, the only reason why using VPN reduce the lag that I can think of is the different route taken. If German players are having connection issues, then I would guess that one of the primary nodes in Germany is having issues, thus using VPN may bypass that node by using a different main route. That would explain why countries east from Germany could have the same issues since there is a possibility that a similar route has been used. Above explanation would apply if problems occur only in a specific region. Different ISP's can use partially same routes as some connection lines are lend so there can be a situation were one ISP lends another its internet lines. I ran some tests in the past and indeed Server is in Virginia US, owned by Amazon so Relic is probably renting services from them, that's not nice since anyone farther away US have a more significant delay, meaning for example that one player can have disadvantage having more considerable delay compared to a player from the US.
The idea of selectively throttling any specific country's IPs is a ridiculous idea.
Changing steam's download server location has nothing to do with the connection with Relic Server.
We tried all the things we could, just to make 100% sure they are not the issue. Tracert goes same way from VPN location as it would be before.
Also the ISP who doesn't have the issues gets routed the same way.
Also we had a patch, where it worked wonderful again for a whole week, then the recent matches fix came up and boom input lag was back on the table.
Cooincidence that one patch makes it go away, then it comes back with the other one?
ISP's changed the routing in that specific time? I don't believe they did that.