AVG formula and Invalid Data Error


I seem to have hit a bit of a pickle (or an afternoon brain fart) while trying to create a roll up.

Essentially what I'm trying to do is create a roll up of averages by month and my formula is returning an Invalid Data Error. I checked the reference columns and they are indeed date columns but beyond that, it should be pretty straight forward:

=AVG(COLLECT({Assigned People}, {Target Date}, MONTH(@cell) = Month@row))

Is there something glaringly obvious that I'm missing?


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