How do I find and fix a “Cannot find #REF!#REF!” error?

Every time I open this sheet in excel it gives a pop up saying “Cannot find #REF!#REF!, which has been assigned to run each time Book1 xIsm is opened. Continuing could cause errors. Cancel opening Book1 xIsm?”

I have a MASSIVE sheet with 10s of thousands of lines on each tab, and I’m really struggling to find what’s causing this error.

I don’t have any macros, I don’t have any workbook links, and I tried using the “error checking” button on every tab but it didn’t find anything. I don’t have any hidden tabs. I don’t have anything in power query.

What could be causing the problem, and how do I find it and fix it? I get this pop up every time I open the sheet and it’s so annoying.