I have been using my Subtronic PRO160 strobes (optic fiber) and Sea&Sea YS-D1 with a Nikon D800 successfully up to shutter speeds of 1/320 (always with optic fiber using a manual led trigger that I installed in a Nauticam Housing, with camera flash sync speed set to 1/320 auto-fp).
I've upgraded my camera to a Nikon D850 in a Nauticam housing with Nauticam's manual led trigger installed as default. Yesterday I've tried my Subtronic's PRO160 UW for the first and they only were able to successfully light each photo if I used shutter speeds below 1/60 (the camera configured slower speed to use with flash in A & P modes). I was shooting in manual mode as ever, flash sync speed set to 1/250*(auto fp) (also tried setting it to 1/250 but no luck). When I used shutter speeds above 1/60 the bottom of the photos became unevenly illuminated or even black (depending on aperture, ISO and strobe power). Strobes are configured to fire with only one pulse from the trigger (as I always use).
Later, at home, I've tested the strobes again and oddly they function normally until 1/200 (but at 1/250 they show the black bar at the bottom of the picture). I also tried my Sea&Sea YS-D1 and they also work normally just until 1/200 (they could have had low batteries so I will repeat the tests, but the Subtronics had full battery in the beginning of the dive).
Anyone has any idea why this strange behavior? Why did they only work until 1/60 underwater? What changes to make them able to work at 1/200 at the surface? Why do they not work at the surface at 1/250 at least? I've tried everything I could remember (Camera in Single shot mode, M mode, EFCS off or on, no shutter delay activated, several combinations of aperture and ISO...).
The only thing that I've changed besides the new camera, housing and new led trigger is the fiber optic cables: i used to use a 3mm optic fiber cable custom made by me (which I didn´t like because they were always failing) and now I use Nauticam standard cables (they didn't work at all with my other led trigger and the Subtronics, although they always worked with the Sea&Sea and also some INON's Z240 that I don't have anymore - all the way up to 1/320 with the D800).
Any help would be appreciated: you never know when you will be busy fiddling with your camera UW and that great white will finally appear and gracefully swim by your side,, :-)