From times to times I face this very much weird issue.
All of a sudden I'm no longer able to access the Sitecore administrator console.
When I type /sitecore
I'm always redirected to the home page.
To bypass this annoying redirect, instead of typing /sitecore
I just type /sitecore/login
and keep moving.
The last time this happened I decided to investigate a little bit more the cookies involved in the issue and realized that by deleting the cookie sitecore_userticket
the bug stop happening.
Using those two strategies I can get rid of the weird issue even it doesn't explain why that happened at first place.