Strange UWTechnics Trigger Behaviour

I have S&S YS-D3 Duo strobes, a Canon R5 camera, an UWTechnics optical trigger, and a Nauticam NAR5 housing. My strobes fire with increasing intensity from the lowest setting to the +0.7 setting. At all strobe settings higher than +0.7 (to full power) the strobes flash, yet the image that is captured is 100% black. Both of my YS-D3 Duos do this. I also have a YS-D1, and it does the same thing (works at all setting from lowest up to +0.7 only). I figure that at strobe settings higher than +0.7 (via back of strobe dial), the timing of the flash gets out of sync with the camera. I've tried it at various camera speed settings and it makes no difference. I have the trigger set to 9 and have carefully programed for the YS-D3 Duos per the users manual.

Any ideas??? Thanks