If it is a checkbox, then it is a multivalue token, which is very different. There wouldn't actually be any line break characters in the content, it just "looks" that way because it is showing all the different values.

Notice that the Forms variable doesn't actually have line breaks.

You need to treat it like a multivalue token, which means you either need to loop through it using a For Each Row and append each value to a token, or you need to flatten it before you do the pattern matching.