Hi,
After updating your mod to 2.2.0 and attempting to load up a save file that was used with previous version I get the following error:
Error while applying migration: Better Axes: Better-Axes_2.2.0.lua
Better-Axes/migrations/Better-Axes_2.2.0.lua:20: attempt to index field 'mk6' (a nil value).
It only happens with saves, on fresh game this error message doesn't show up.