You can clean your project deployment directory also you can close 'login-with-mendixsso-button.html' file.
Try the following scenarios:
Hope this helps!
Are you using something like Microsoft One Drive or similar software that backs up files in real time? This sometimes causes problems with Mendix as it is trying to synchronise files as Mendix is building and moving them. If you are, try disabling it, or moving your Mendix application to a location that isn’t automatically backed up.
Hope this helps.