I haven’t gotten around to messing with the Yezl Y3 driver. It seems pretty typical in construction IIRC, it’s a QX9920 based buck driver. QX9920 is entirely capable of blowing emitters though. RMM has discussed the problems with QX9920 based drivers some in ImA4Wheelr’s Driver Mod: HX-1175b & HX-1175B1 (Pic Heavy) thread.
It’s not a “voltage spike at startup” thing so much as it is constant voltage spiking. The output is probably not clean at all. Your DMM will not be able to indicate dirty power or it’s form to you. Observing the driver’s output on a scope is really the thing to do. As you bring the set current up the bad behavior should be visible on the oscilloscope before it gets to the level where it kills emitters.
The MT-G2 is much more resilient than the XM- or XP- series emitters. It is not a very good measuring stick when trying to determine whether you have a driver which kills emitters. (eg not killing an MT-G2 on 2s or 3s very likely proves nothing)