Constantly getting "Failed to Connect to Instance"

Since roughly 2 weeks ago, the servers have gotten increasingly unplayable for me (an EU-based player).

First, there were intermittent lag spikes which I could circumvent by moving from the regular EU servers to Moscow. Then, last week, I started getting more and more "failed to join instance" errors. Since yesterday, I'm getting "failed to connect to instance" errors, and not even going to the Moscow or Washington DC gateways fixes it anymore.

My hardware and internet connection are perfectly fine, don't have any issues in any other game or application, diagnostics didn't show any errors, packet loss or anything like that. Until yesterday, playing was still possible by sacrificing latency and going on non-EU servers, but now, the game has become literally unplayable for me.