[PC] Push to talk not working

Not sure why, but my Push To Talk doesn't work. I've got it mapped to default 'U', but when I push it, my team don't hear me and do not see my username appear in the right-hand side. Surprisingly, I see my username appear, which is strange.

I've made sure my microphone is the default device in Windows. I've changed the "exclusive use" options in the advanced settings. It works fine in TeamSpeak and Skype. The issue remains even when I boot my machine and ONLY open Siege (through Uplay).

Anyone else having this idea?