One thing to try is get a Multi-meter on the 24V and see
what that output is at higher RPM, should be in the ballpark
of 28V. You could also try knocking the voltage down with
a diode or two in series with the 24V feed on one light and
see if that light then holds up longer than the other. Each diode
will take you down about .8V or so, pick a ~4A diode. This might
be enough to prove it's a voltage sensitivity. You may have a
defective pair of lights -- not impossible they got a run with one
or more incorrect parts stuffed on the converter board

Maybe scream foul anyway and get two replacements, maybe
they fess up and admit there was an issue

ron