Why am I receiving #INVALID OPERATION error in some of my sheets

I have multiple sheets with the same columns (Health, Task Name, Start, Finish). Note that the Health column is a symbol (red, yellow, green, blue). In my summary sheet, I am using the following Index Match formula to search for Task A in Task Name column and spit out Health.

=INDEX(Health:Health, MATCH("Task A", [Task Name]:[Task Name], 0))

However, on some of my sheets, I am getting #INVALID OPERATION error and I can't seem to figure out why.


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