The same project (with same maven configuration and same classes) is working for me and opening http://localhost:8080/swagger-ui/index.html endpoint correct.

It seams to be "IDE magic" (i suppose you to using one), try to close IDE and start it, then rebuild and rerun your project.

Perhaps there is firewall in your local machine and it cause such "magic" for opening .html pages...

Also, try open above swagger link in several browser, there may be a reason in your browser settings.