Those 2S drivers should definitely have a C3, as recommended by DEL. I also have a C4 on the one I just did.
This post has his Yezl Y3 2S board with the C3: https://budgetlightforum.com/t/-/44006/152
DEL's take:
- 3 goes across Bat+, Bat-. Basically where C1 used to be. 4.7 uF or 10 uF should be good.
- C4 goes across the FET (drain to source). Should be 0.1 uF, bigger will be counter-productive.
Both help to suppress the inductive spike seen at FET (and even 7135) turn-off. They do not seem to be necessary for 1S lights, but both you and Tom had failed 7135s with 2S.
Here: https://budgetlightforum.com/t/-/44006?page=6, post #189