Keybind not working - ctrl + mousebutton 12

Hi there community!

I've been playing World of Warcraft with a naga trinity, and recently had a strange issue: i can no longer bind ctrl + mousebutton 12.

Even stranger, this combination works with every other mouse button, just not with 12.
So i can keybind ctrl + mousebutton 1-11 .. but not 12.

The button 12 works by itself also, as does the ctrl button on my keyboard. The combination however does not work.

Anyone have an idea of why this is the case? Thank you in advance! x