I'm having the issue as well. It also started on Sunday for me. Everything was fine, then I was disconnected from a dungeon, (So was everyone else in my party) but upon logging back in, I had huge lag spikes that last 10-20 seconds each, every few seconds. I also get disconnected after "playing" for about 20 minutes. This issue has rendered the game completely unplayable, as I'm unable to do dungeons, quests, or even mine. The chat log seems to work fine at all times.

I've run tests that confirm that the problem is not with my ISP or connectivity.

I'm playing on Hyperion (NA/EU server) from Japan.