I'm having to shoot as low as 50th of a second to avoid the line in the middle, where the top half of photo is lit and bottom isn't. I was able to shoot at 125th of second in the past...not sure why I can't now.

I'm not using a nikon strobe or pocket wizard brand. But the strobe is firing each time, it recycles really quick. And the remote must be working because the strobe is firing.

There is no pattern as to which photos are lit and which ones aren't. Sometimes 5 in row will be lit, then 2 aren't, 1 is, etc..

Since everything was working perfect for me a few weeks ago, I'm afraid I changed a setting on my camera and I'm not sure what?

Thanks for your help!