Perhaps different Apache versions? I don’t have many problems with XAMPP and InfinityFree. Some things don’t work on XAMPP because I haven’t enabled some directives but it doesn’t cause any problems with InfinityFree.
Because creating a new domain probably won’t fix much.
Yes, it is.
You’re going to have to debug your code yourself. I don’t think anyone would be willing to go through all of the htaccess file and pinpoint every error. Please read the article that Admin posted: