$arch is not interpolated in @host.url_for_boot(:initrd) and @host.url_for_boot(:kernel) for suse based systems.

For example, I have $arch instead of x86_64 when viewing the template for a host which is suse based

I think the issue comes from there :

https://github.com/theforeman/foreman/blob/develop/app/models/operatingsystems/suse.rb#L12

Let me know if you need more infos