The game crashes on world load/generation if Sniff's Weapons is present but The Undergarden is not installed (it tries to create the Creative menu for the Undergarden compat items and fails). I am using the latest version of both Extra Compat and Sniff's Weapons at the time of writing. I am on NeoForge 47.1.106

Are you sure you are using version 1.5.22? I tested using just Sniffs Weapons and Extra Compat and there were no problems