I am trying to build my finished react app from the terminal using npm run build

When I do this I am met with the following error:

TypeError: Cannot read properties of undefined (reading 'toLowerCase')
    at Array.some (<anonymous>)

I have looking into a couple of documents here and here and they state that the error is produced when calling the toLowerCase() method on an undefined value.

Unfortunately When running a search across all my documents for the toLowerCase() method no results are found.

I am not making this function call, what is the best method for debugging this further and why is this error occurring?

Thanks