I imagine you're using CLR browser. It doesn't show anything at all when you visit http://html5gamepad.com/? Also, do you have the latest version of CLR as listed on https://obsproject.com/forum/resources/clr-browser-source-plugin.22/?This used to work fine but it doesn't seem to detect my controller (PS3 on USB detected as a wireless XBox 360 receiver through DS3Tools) but my games work just fine. I also tried that http://html5gamepad.com that M1K3_Alt3r mentioned but no response there either.
Any idea what may be wrong?
I'm also curious about what URL you're using to access the viewer as well. I recently changed the address and had all the old URL forward to the new one but sometimes there might be some issues. I doubt that's what's causing it, but who knows. In terms of what may have actually gone wrong, I'm not very sure. CLR in its own right is ages old in terms of software updates, and OBS Studio now ships with an up-to-date browser plugin being managed by the project itself. I'd suggest at least trying out studio and seeing if the viewer works there to sort out any CLR specific issues. I imagine the site also works fine when you access it regularly via Chrome as well?