I searched around and saw it might be related to SharePoint not being in the exceptions list but it is already setup on our IE by default.
This is in Nintex forms version - NFO 184.108.40.206.
Is there something special that needs to be done to get IE to load the file?
Part of the problem with mine was an incompatible arrow function. It would cause my include file to not work but not give me any error and the arrow function was working fine in other browsers.
If you look in the browser console when trying to load your form does it give you any error message for the includes file?