This doesn’t seem to be affecting everyones sites, so one work around in the meantime, (and I fully appreciate this not the most convenient way), is to create a new fresh project, and copy and paste the major elements from your old site, onto the new project.
You should then be able to use and style the navigation as expected. If you need any help with this, then please let me know.
There has been a fix pushed that has fixed the issue of your current tab in the navigation. I’ve tested with your site and you should now be able to select a page for the nav-link and design it’s current state.
If you have any further issues, please do not hesitate to let me know.