I tried the standard / node and a code block divide and all my inputs look good but the first operation on a list comes back null…the rest are fine??
Can you upload an image of your graph so we can see what data you are working with? Otherwise it is nearly impossible to guess why you are getting a null on the first index.
Can you use Object.Type to make sure your inputs are numbers? That’s likely not the issue but worth a try.
Also, have you tried just closing the graph and reopening it again?