I have a Yongnuo YN560IV with RF603CII trigger.
I have the weirdest problem. Flash fires fine without anything attached to the head, or with my Gary Fong lightsphere or another cheapie mini softbox strapped on. But when I use the black Gary Fong speed snoot, AND WITH THE GRID ATTACHED, it suddenly stops working! So bizarre. It's a piece of plastic. Do speedlight flashes generally have a light sensor that prevents them from firing into darkness? But it works while attached to camera hotshoe. So it's a wireless/darkness combo issue I think.
When it doesn't fire, the flash unit still makes that whirly recharge sound and a beep to say it's ready again. So clearly getting some kind of signal.
Tested extensively. Occassionally (<5%) it will work with it on, but that's the exception.
Even though the manual says to put the hotshoe transmitter unit on TX, it also works on TRX. So I've tested extensively on both settings. Changed radio frequencies, changed batteries, all the usual troubleshooting stuff. Literally no settings changed from when it fires one moment without the modifier on to the next moment I put it on and it stops firing. Then i quickly pop it off and, boom, flash fires again.
So nothing to do with camera settings is what I mean with all that too.
If someone has any ideas how to get around this I would greatly appreciate it!
Camera is Fujifilm X-T2 if that makes a difference.