error parsing JSON at line 0

Well this sucks.
My first game is nearly finished and suddenly my save system has died. Don't know why - once it was working, I didn't edit it.
Got this error:

E 0:00:04.926   get_as_text: File must be opened before use.
E 0:00:04.927   call: Error parsing JSON at line 0: 
  <C++ Source>  modules/gdscript/gdscript_functions.cpp:1215 @ call()
  <Stack Trace> Globals.gd:122 @ _load_function()
                StageSelect.gd:10 @ _ready()

I already have error handling built in with a default value function should there be no save. It's been working this whole time until just now.

Global Functions:

func _save_data_update(): ## compiles data
	_saveData = {
	"_thoughtsCleared" : _thoughtsCleared,
	"_secondsStillness" : _secondsStillness,
	"_lilypadsKissed" : _lilypadsKissed,
	"_blossomsWatched" : _blossomsWatched,
	"_momentsOfSilence" : _momentsOfSilence,
	"_centerBalance" : _centerBalance,
	"_breathsTaken" : _breathsTaken,
	"_wisdomRead" : _wisdomRead,
	"_splashesCreated" : _splashesCreated,
	"_zenAchieved" : _zenAchieved,
	"_mandalaRotations" : _mandalaRotations,
	"_globalMusic" : _globalMusic,
	"_globalSine" : _globalSine
	}
	return _saveData


func _save_function(): ## saves to file
		var _myFile = File.new()
		_myFile.open(_GAMESAVE, File.WRITE)
		_save_data_update()
		_myFile.store_line(to_json(_saveData))
		_myFile.close()


func _load_function(): ## loads if present (logic in main scene)
	var _saveFile = File.new()
	_saveFile.open(_GAMESAVE,File.READ)
	var _text = _saveFile.get_as_text()
	_saveData = parse_json(_text)
	
	_thoughtsCleared = _saveData._thoughtsCleared
	_secondsStillness = _saveData._secondsStillness
	_lilypadsKissed = _saveData._lilypadsKissed
	_blossomsWatched = _saveData._blossomsWatched
	_momentsOfSilence = _saveData._momentsOfSilence
	_centerBalance = _saveData._centerBalance
	_breathsTaken = _saveData._breathsTaken
	_wisdomRead = _saveData._wisdomRead
	_splashesCreated = _saveData._splashesCreated
	_zenAchieved = _saveData._zenAchieved
	_mandalaRotations = _saveData._mandalaRotations
	_globalMusic = _saveData._globalMusic
	_globalSine = _saveData._globalSine
	
	
func _default_stats(): ## default levels if nothing present
	_thoughtsCleared = 0
	_secondsStillness = 0
	_lilypadsKissed = 0
	_blossomsWatched = 0
	_momentsOfSilence = 0
	_centerBalance = 0
	_breathsTaken = 0
	_wisdomRead = 0
	_splashesCreated = 0
	_zenAchieved = 0
	_mandalaRotations = 0.0
	_globalMusic = true
	_globalSine = false

And then here is the function called at ready at the main scene:

func _saveCheck(): ## if no save file, load default values
	var _playerSave = File.new()
	if _playerSave.file_exists("user://gamesave.json"):
		Globals._load_function()
		print("User data loaded!")
	else:
		Globals._default_stats()
		print("Default data loaded.")

Weird thing - it's crashing at the end of an animation signal, not on load. There's no memory function there.