So, just to add my suggestion to the pile:

Try a VPN. Seriously. I've had a lot of people that complain about abrupt 90k errors, such as when they hit "commence" on a duty or teleport or some other circumstance, and the issue goes away.

That's not to say it's 100%, it's not always what's wrong - but if you haven't tried it, I strongly suggest giving it a go and then it's at least one more thing ruled out.