The MtnE drivers, though good for their time, have been outdated for a few years now. Richard doesn't participate on the forum anymore. One of the important things a member DEL came up with is adding a 4.7 ohm resistor between batt+ and the diode. There should be resistor(s) on the FET gate as well - I don't see them on your pic above on post #4.
Again, the driver design is old and outdated from what we've done and learned since.
Check out DEL's OP in his driver thread here: https://budgetlightforum.com/t/-/44006
DEL isn't on the forum anymore but his design tweaks live on in countless # of driver designs that followed. DEL designed the buck driver in use on the BLF GT.