Well, I have to eat my own words. It's happening with the other servers I'm on as well.
So I'll be offline until I can figure out what the problem is and fix it. And before anyone asks:
1) Yes, I have Shiny Water turned off. It's always been turned off.
2) Yes, I've tried minimizing all of my video and graphics settings. No good.
3) Yes, my graphics card drivers are up to date.
4) Yes, I'm running Windows 10, and it's up to date.
5) I'm running Malwarebytes Anti-Virus Premium, and yes, it's up to date too.
6) Yes, I've tried turning Malwarebytes off while I'm running NWN Multiplayer. No good.
7) Yes, I've tried running NWN right after shutting down my computer, waiting fifteen seconds and turning it back on. No good.
8) I've also tried installing a fresh copy of NWN Diamond on another hard drive, copying all of the Haks, Tlks, Overrides, CD Key files and so on over, and running the new copy. It has the same problem.
It may be a modem issue. I'll try reseting my modem next, then I'll go from there. Wish me luck.