Hi @Anthony_Fransella
The reason is exactly what you stated, when there are multiple fields they are converted to a comma separated string which looks like this
Product1,Product2,Product3
while Airtable expects only 1 product and it cannot create a new product called Product1,Product2,Product3 because it appears to be a formula field in Products table.
They way to automate this is to use Looping by Zapier so you can update all 3 product records and not just 1 product.