That's strange. The resistor has been the single thing to make the big difference. Looking at the Lumintop EDC18 driver (same design as the FW3A) last night. I noticed 3 caps of 3 different sizes to ground - this is a common for reducing spikes. The one cap, we use across the MCU V+ and V- should be as close as possible to the pins - I know DEL emphasized that, posted here:
https://budgetlightforum.com/t/-/39069/1103
This refers to C2, the 0.1 uF cap, schematic:
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A lot is explained in DEL's driver thread's OP here: https://budgetlightforum.com/t/-/44006