Can’t you do the same thing by dropping a browser() into a function you are applying to each element in a list?
I think FP is good for more concisely expressing simple stuff that's unlikely to break. Don't really believe in using it as a complete replacement for loops.
Or - once you’ve found what element in your list is causing the issue- extract it and feed it to your function with your debugger on.
Admittedly I have often had a more challenging time fixing FP code than if I had used a for loop. This might be because I am not as familiar/comfortable with FP than procedural flow.
There has to be a for loop eventually. But crawling through a for loop within a procedure can also be painful if there are many different case scenarios. You could counter that good code wouldn’t suffer such a problem, but if the code was good it might not have been broken!