If I move the window to any monitor to the left of the main display the window becomes stuck and can no longer be moved.
I can temporarily fix this by either changing the main display to the left most monitor or enabling Nvidia Surround… but having to so every time I load up clients is a bit of a pain.
Can also shift it to another monitor with win+Shift+arrow and rearrange but the main issue is you can't even more the spell/inventory windows around either.
If I remember correctly this is a known issue (having the client to the left of the main display) and rdragon said it's actually a bug in activeskin and not in the Realm client so is out of their ability to fix
Known issue. It's in one of the patch notes. Supposedly they're working on it. I actually ended up just moving my second monitor to the right to get around this. You're only other option would be to run the game in a virtual machine, but that's probably even more of a pain than the other workarounds available.