36x LED 5730 in series: diodes burnt when LED driver (based on BP9833A or MT7854BD) powered up
I think it's because you attempt to use these constant power (18W) power supplies at or near their maximum voltage. It should be used closer to the minimum voltage. And/or because you use constant power and not constant current power supply.
When you try at the upper voltage limits, the driver doesn't see 18W even thought it outputs 120 mA and rises voltage much higher in order to reach 18W.

You need a constant current power supply for exactly 120 mA (Not 100~240 mA or the likes) with a power range between 15W to 30W. Then theorically it should outputs a voltage within the LED limit.
The goal should be to keep 120mA, not 18W or x volts.

Besides, I advise you to divide the series and use two or even three series in parallel, each with their own suppy. It's an extra cost but it's much safer against electro shocks. At 120 VDC it's already quite dangerous.