I have a Canon 5D Mark IV and mid shoot the camera stopped talking to the transmitter. Since then, I've tried everything. My hotshoe works - it triggers my 600EX II RT flash perfectly. Using a sync cord with my lights works just fine (I use both White Lightnings and Dynalites). All the remote triggers I have (cybersync, pocket wizard, and one other I can't remember) all work when I hit the test button, but none will fire when I hit the shutter release. And it's super strange it happened mid shoot-was working perfectly before that (and always has). I'd love to escape using my sync cord, but that's the only thing that is working right now. Any suggestions/ideas?
Perhaps something is interfering with the wireless signal from your hotshoe transmitter. A lot of stuff operates in the 2.4 ghz range and a strong signal from another device will wipe out everything else. Try holding your camera very close to one of the receiver equipped lights and see if it fires.