MONTH() and YEAR() functions return #REF, and the "Month" and "Year" filters on pivot tables seem to be the issue.

I am trying to use the MONTH() and YEAR() functions, but whenever I type them in this specific sheet, they seem to autocorrect to "Month" and "Year" (the first structured reference option in the select drop down that appears as you type) and produce an error, even when the function option is explicitly selected. Typing "=Month" alone produces an array of dated data from elsewhere in the sheet, which seems to indicate that it's reading it as a structured reference instead of a function. The functions work normally in a fresh file (even when referencing the same data in the original file). Is there a way to indicate that is should be a function, and not a structured reference?