Having firing issues with Sb-900

[Hooligan Dan]

So I used it on camera last night with no problems but I went to use it today and it's not firing while on camera.

It fires if I hit the test button. It fires if I put it on remote and use the on camera flash as the master and it fires if I use the SU-800 as the master. But it doesn't fire if it's on camera as master or regular.

Any thoughts?

EDIT: I should add that if I put my SB-600s on the camera they work fine.

 

[KmH]

For some reason the body and the speedlight aren't communicating.

 

[Hooligan Dan]

Center contact seems fine by all outward appearances. Interestingly, the ready light still flashes after I trigger the shutter even though the flash doesn't fire.

 

[Hooligan Dan]

And now, after a bunch of times of testing it on and off the camera, I just attached it again(after having just taken it off when it didn't work) and it works fine.

I wonder what the deal is.