Shadowplay related problems are discussed in detail in the following thread at the official site, check it out: https://forums.geforce.com/default/topic/628497/shadowplay-quot-switch-on-quot-button-does-nothing/
Nah this isn't the issue we're (I am) having. Shadowplay plays nice with Counter-strike Source and Left 4 Dead 2...
The problem is selectively happening with Watch Dogs and Tom Clancy's Ghost Recon Phantoms.
[strike]Only thing I can conclude for now is that [on my machine] it works with older games, but not with these two recent titles.[/strike]
UPDATE
Your link did steer me in the right direction.
Here : https://forums.geforce.com/default/topic/628073/geforce-experience/shadowplay-feedback-thread/
I found this : 1. It seems you can only record in fullscreen mode, is there going to be support in the future for windowed/borderless windowed in the future?
So I changed to fullscreen and it started recording when I hit the hotkey!