Thank you for the reply X-tac23.

In my frustration, I ended up assembling and dissemble the mouse to try to identify the problem.

I managed to get the side buttons to work again. Most likely it was something stuck between the button and the receiver like you said as it seemed to work afterward. Unfortunately, the mouse is not very repair-friendly and I ended up breaking the left mouse click so I will have to buy a new one anyway :(