On the face of it I would say that it's because 2.3 changes the way arrays are references.
It should be :
global.spells[e_spell_types.heal][e_spell_stats.min_value] instead of global.spells[e_spell_types.heal, e_spell_stats.min_value]
When I loaded up the December 2019 download I was able to play the game but I noticed some bugs and I've decided I'm just going to re-write most/all of it so that there are no more bugs (that I know of) and that it works properly with 2.3. It will have the benefit of another years worth of coding experience + be created in 2.3.
This does mean that it will take some time for me to update the files so if you'd like to refund in the meantime that's no problem.