All-pass not working with Harlowe 3.3.3

So, hey! I'm trying to create a game about ancient Assyrian doctors where you diagnose a sick patient. I'm writing a series of dropdowns that look like this:

HEAD

(dropdown: 2bind $head1, "nothing", "fever", "dizziness", "shortness of breath")

{(if: $head1 contains "fever")[(set:$head1Diag to true)]}

And then, on the next page, trying to use the results of the dropdowns to create a challenge the player has to pass, like this:

(set: _symptoms to (array: $head1diag, $head2diag, $torso1diag, $torso2diag, $legs1diag)

)

(if:(all-pass:_symptoms where _symptoms is not false))[

(set:$diagnosed to true)

You think you've got a good list of the King's symptoms now.

[[Let's put them together.|diagnosis3]]

]

(else:)[That doesn't sound right. If you're having trouble remembering what ails the king, check your [[case notes.]] ]

This isn't working. Every time, regardless of what I put in, the game lets me through.

Can I get some advice about what it is I'm doing wrong?