So I decided to try another Data Center.

I am located in the United States.
I created an alt on the Chaos Data Center, Ragnarok Server. Completed the level 1 MSQ, then just ran around town a bit.

Exit the game while on this character... logged back in and successfully connected again w/o any hiccups.

Logged out and tried getting back on my main on Primal Data Center, Hyperion Server... Error Code 10105.

Booted back to start menu, immediately switched back to Chaos Data Center and logged back in w/o any hiccups...
I then logged out of this character again, and logged back in right away...

So what gives? If it's my ISP how am I able to repeatedly, and successfully, connect to a completely different data center?