Clear cache and cookies

Enable cache from Develop menu:

From your Safari menu bar click Safari > Preferences then select the Advanced tab.

Select: Show Develop menu in menu bar

Now click Develop from the menu bar. From the drop down menu click Empty Caches.

To delete cookies.

From your Safari menu bar click Safari > Preferences then select the Privacy tab.

Click Details then click Remove All then click Done.

Quit and relaunch Safari.