It seems to happen when I use my Y button on my XBox 360 controller (it's not an official controller - VOYEE brand). I'm also running JoyToKey so I can use my left joystick to use as a second D-pad. Here's the message that pops up.
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ERROR in
action number 1
of Other Event: Animation End
for object block_obj:
unable to convert string "left" to bool
at gml_Object_block_obj_Other_7
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gml_Object_block_obj_Other_7 (line -1)