I have 5 YSD2 strobes and I have experienced poor reliability.
Strobe 1: Flooded while soaking in bucket after a 3-dive day. No issue all day (no flood), soaked for 20 minutes at home, one flooded strobe. Did not flood during the dives as it fired until the moment I ended the dive, rinse bucket for sure.
Strobe 2: Randomly blinks power light indicating strobe is about to die regardless of charge. If i realize while it is blinking, I can turn it off and then back on and it is usually fine. If I do not see it blinking and find it off, but the power knob is still in "on" position, it has to come out of the water and have the batteries removed to restore. Strobe is gone for the dive.
Strobe 3: photo-sensitive diodes in strobe fiber receiver no longer working; cannot fire the strobe via fiber anymore.
Strobe 4: Works fine.
Strobe 5: Out of the box it would not fire at all via fiber. Troubleshot with the LDS and another photo pro where I live. Returned to Sea&Sea. They argued that there was nothing wrong with the strobe and then eventually admitted it was programmed into a "custom" mode that would not work with synchronized cameras. I do not think this is accurate as it was not a bad sync issue, it would not fire at all. I had to eat the shipping twice and it took 4 months to resolve. Very poor service.
These are all YSD2 Strobes, yellow body indicating made in Japan, but not with the "J" printed on the body. These are about 2-3 years old.
Sea&Sea denied any level of coverage for the flooded strobe without inspecting the strobe despite covering floods from defects.
I am trying to resolve the photo-diode strobe with Backscatter now, but I suspect no positive outcome there but I cannot say with certainty.