Issue with targetting, help identify cause please

Hello.

I'm using a logitech g600 mouse for targeting partymembers/arena123.
95% of the clicks on the mouse results in me targeting as intended, but sometimes in conjunction with modifier shift (1-2 seconds after pressing shift) the mmo-buttons on the side does not respond. This started occuring after i reinstalled windows. I tried updating the driver for the mouse, but after realising the thing with the shift-modifier, i'm really confused.
It's not because the button doesn't work. Shift interferes with something it seems. In keybindings i have both the normal bind and the shiftmodifer version of the bind, so it should work for both.
Let's say i press the keybind for targeting myself, i use some spell with a shiftmodifier and immediately try to target party1: Then i have to spam the key for targeting party1 for a couple of seconds before it goes off. This is very annoying, and it sometimes causes me to lose a game because i randomly PS a wrong target or something.
Anyone has any clue what causes this?

Thanks in advance. I use a Roccat Arvo keyboard btw.