Hi guys,
I've got the same kind of issue with my D750 + SB-900 in CLS
But for me, the camera just don't shutter at all oO
Sometimes I have to wait 10-15s and I can't even shutter...
I used the CLS for long time on my D7000 with SB-700 and I never got this problem...
I've spent the last hour testing and apparently it's caused by the overheating security on my built-in flash !
I usually set the built-in flash so it doesn't affect the final picture (it's firing a tiny bit before the actual picture to don't appear), bu I think this make it fire at full power.
When I simply set it in Manual mode and on 1/128, I can shot much more before I get the same issue.
I have to try again with my FM transmitter to test it, but I guess I won't have the same problem (only SB-900 not firing when it's recycling)