Also found this bug:
___________________________________________
############################################################################################
ERROR in
action number 1
of Step Event2
for object WaveSpawner:
Data structure with index does not exist.
at gml_Object_WaveSpawner_Step_2
############################################################################################
--------------------------------------------------------------------------------------------
stack frame is
gml_Object_WaveSpawner_Step_2 (line -1)
which crashes the game (it has happened to me twice)