thumb button on mouse suddenly not working?

I’ve been using this mouse for a while now (around a year) and randomly, the one of the side thumb buttons stopped responding.
Every other button works except button 4- the one on the right when looking at the mouse from the side. I’m not sure how to fix this honestly, and I’ve had the issue before with the same model of the middle mouse button and scroll not working- this is the replacement I bought.

I don’t have the ASUS Armoury so fixes through there are inaccessible to me, and all the drivers for the mouse are up to date so I don’t know if its a software or hardware issue.