Ouch, that GaN has seen better days. Not cheap either - what happened?

We originally designed the converter to operate at 110VDC input. However, during the initial test, we used a 60VDC power supply and tried running the same rated output power with the 60VDC input bus, which caused a higher current through the GaN device. This, along with the lack of a heatsink on the initial test is what we think caused the failure.

https://www.mouser.com/datasheet/2/692/GS66508B%20DS%20Rev%20160202-913400.pdf yah they're about 17$ on mouser.