This is embarrassing, but the problem completely unrelated to anything mentioned in this post. It was a stupid mistake made by my own bad programming habits in combination with a typo.
In my original ask I changed the name of my local variable from processorToolStripMenuItem
to newToolStripMenuItem
since this made more sense out of the context of the application. The item I was adding it to was a field named procesorToolStripMenuItem
which as you can see is missing an 's'.
For the line of code setting the keyboard shortcut I made the same typo and was thus setting the keyboard shortcut of the wrong thing. They should never have been named something so similar to one another in the first place.