Hi dwolfeman,
What you are seeing is correct, the NSUR plugin will temporarily take you to the main site to register and then bring you back to the subsite after registration. This is because on a Network (or otherwise named as a Multisite installation) registration by users is for the whole network.
From your site I see that you have a subsite with the domain name whitehorsemissions which goes back to register at resilientword which is your WordPress main site install. the way to get round this is to use https://www.ads-software.com/plugins/wp-multi-network/ and create a WordPress installation that is a multiple-Network WordPress installation (or “multiple-multisites”) you can then create a new Network using whitehorsemissions.com as the primary site for that network, then if you had a future need for more subsites under whitehorsemissions e.g. whitehorsemissions.com/subsite1 whenever people register on whitehorsemissions.com or whitehorsemissions.com/subsite1 they would always be sent temporarily to whitehorsemissions.com to register.
To conclude its not an issue with NSUR but just some rework on architectural changes to your site using wp-multi-network that is needed.
installing wp-multi-network you can create new Networks easily within your WordPress installation, however, one thing that I’ve not managed to succeed in is to create a new Network and use an existing site as the base site of that Network (which is your case). In these cases I’ve always created the new network and moved all the content from the existing site over to the new Network primary site. You may have more luck with that but that’s what we’ve found is the most robust route.
Please note always backup your site and data before doing this to have a roll back plan.
..Justin