Help--Sea & See YS-D2 not firing? Ideas?

[ReadyDiverOne]

Hello, here in Grand Turk on 4th day of diving and one of my S&S YS-D2's won't fire. It's been working fine all week and, unlike others, I've never had any issues with either of them. Batteries are fully charged, yellow light is on, tried new strobe cords (firing from flash of RX100-V, but I get nothing. Have re-inserted batteries, used 3 different strobe cords, nothing.

Ideas??

Thanks.

 

[ReadyDiverOne]

Update: so I shoot in Manual mode, which with the RX100 and the S&S strobes is the first position on the strobes, the double/pre-flash position which lights up yellow. Turns out that's the only mode not working: both the next mode single flash green light and TTL mode (blue light) are working. So I will give TTL a try and see how that goes.