Those with periodic error 90000: do you have a Realtek network adapter?

[Noah_]

Fixed:

After disconnecting with error 90k on an hourly basis and trying everything else, it looks like the culprit was automatic updates setting on Windows Update (which I now have scheduled for a certain time) or the automatic updates / running at startup of Easy Tune 6, my motherboard's chipset program. One or the other, but probably ET6. Since changing the Windows Update setting and changing the ET6 setting and closing it, I've had the game connected for about 10 hours straight with no disconnects while testing the connection.

grats on fixing yours, sadly for me it is not the windows update that's causing it, because I don't have it turned on.