Why does this formula give error?

I don't understand why I get an error with this formula. It is this:

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If necessary, I can try to mock up a demo of the problem, but I'm hoping that the formula and little context information is enough. This is in Excel 365. Here's what I have found:

-- If I put the the range from the formula into its own cell, it evaluates correctly. That is,

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works in its own cell.
-- If I refer to the cell containing the range component instead of putting the range into the formula directly, it works. That is, let's say I put

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into, say, D1, and then change my initial formula to:

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. That works.
-- Putting the range into the formula, as shown initially, gets the popup error "There's a problem with this formula. Not trying to type a formula?" etc...

What am I missing? Like I said, I hope that explanation is enough, but it won't let me save the "incorrect" formula, and it will take a bit of time to put together a demo without customer data.