The neutral wire coming from a GFI can't be gang attached or swapped to or with any other neutrals. the neutral coming from the GFI they had terminated (wire nuted off) and then picked up the neutral from the cooktop. Can't do that. Its not uncommon to see all the neutrals in a gang box twisted together which would normally work but not with a GFI circuit. Separate the neutral for the GFI. This won't make sense until you take the drawer out and look in there. In mine the circuit you are looking for was on the left side of the double gang box and marked with a single wrap of black tape. the TV circuit maked with yellow tape Frig was Red tape, cooktop was double black tape. Hope that helps.
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