I've put up a new version(1021) that I think fixes the issues. Please let me know if you run into any further issues.
I updated and beat the zoo level but then had another hard crash while the bad guy was talking to the fox:
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ERROR in
action number 1
of Step Event0
for object obj_npc_fox_swamp:
Pop :: Execution Error - Variable set failed burn - read only variable?
at gml_Object_obj_npc_fox_swamp_Step_0
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gml_Object_obj_npc_fox_swamp_Step_0 (line -1)