FN Keys not working

Hello there,
since recently I have following problem.
The multimedia keys, which you use by pressing FN+F(Number), are not working anymore on my Razer Ornata Chroma. Also the side wheel buttons on my Razer Mamba TE are not working too, when I use a custom key combination ( I have them set to CTRL+TAB(+Shift) to maneuver tabs in chrome ).
When Razer Synapse isn't active the multimedia keys do work on my keyboard, but obviously the buttons on my mouse are set to default (scrolling up and down) and the light effects are off/set to default.
I tried reinstalling Razer Synapse multiple times with no success and I really don't know how to fix it.
Can anyone offer some help?
Thank you!