"unable to connect to the log-in server"

Before I blame my connection, I've already tried both DSL line and 4G mobile connection, both results to the same error on the GW2 launcher: "The game client was unable to connect to the log-in server. Please restart your client and try again."

Also I was getting unusually high ping and disconnection from the last game session for the past 20 minutes, something I have not experienced for a pretty long time. I mean actual 3-second ping displayed in the options menu, not some weird downstream delay coming from your servers. Nothing else is taking up bandwidth on my internet connection, only just a normal 40KB/sec coming from the world boss session.

There must be something happening that's out of my control.

You can use a program like Pingplotter to assess where your connection issues lay.

Good luck.