Hi,
This seems to be strange.
I tried doing this again on my PC. I found no issues.

How about making sure about the following.
1. Create 1 Route at a Time. Save Changes. Refresh the page and try adding new Route.
2. Make sure while creating new route no check boxes are selected under Static Route.
3. Try using another browser / incognito mode of the browser.
Hope this helps.
Regards,
Ajit
AjitsNW@gmail.com
www.ajit.network