Comfychair was just cross posting the info in that thread. This is the main thread for that testing project: FETs and gate resistors - scope images. [Post #1045 ~= Post #55 there]
Just to be clear, the post you referred to contains two configurations (marked V1 and V2 in red text in the upper right corner). Which one you are you using?
Regardless of what you have now I’d try the other config! V1~~V2 or V2~~>V1. They aren’t really versions, just different configurations.
I assume that you are using 1s, not 2s or more (zener setup). If you are using >1 battery in series you should let us know. What current level are you achieving on your highest level? Higher currents should create a larger field resulting in a larger spike as the FET turns off. This may require more capacitance between B+ and GND.