I'm trying to make something starting with the LTC7060 example design and so I just removed some extraneous components/connections then raised the high-side voltage. Lower voltages (<40V or so) had no issues and continued to work as expected with the voltage across the load going from 0 to whatever the high-side voltage was. But over 40V, the high side is unable to stay on over the period of the square wave input and instead gets spikey. The low side works as expected. What might be causing this to happen?
I've also tried not changing anything in the example circuit except for the high-side voltage which presented with the same issue so the schematic below is just the minimum components to reproduce the issue.
Schematic:
Sim results (voltage on R3):
