I have been having a deteriorating issue with skill combinations for my Berserker not working.

I can no longer get buffing skills S+LMB, S+LMB+RMB and S+ RMB to work. 

Is anyone else having issues like this, are there any known issue like this?

That sounds strange. Are you sure your S key is working in game? Is it perhaps reassigned? Also make sure you have your offhand equipped, always have enough Mana, and do not have the skill locked in your K window?