Hello all,
As the title says my mouse thumb buttons (mouse4 and mouse5) do not work in-game.
I changed peeks left and right for those buttons within the game, and my user.ltx shows the change as well.

As of now I have no hotkey or scripts or anything like that added.

If it's useful, here's my SoC setup:
ZRP 1.007 r5 i think
Absolute Nature/Structure
Weather Overhaul
Shaders MAX
Light HUD
Some mod that changes how the weapon is shown in-game

I've found a solution through an outside program.
X-Button Mouse Control works well will this as well as The Witcher 1, for future reference.