I recently had the problem, that my admin toolbar would be disappearing randomly. This of course can be a major problem – how do you want to administer your drupal installation when there is no toolbar? Only emptying the cache helped – so having the url to empty the cache at hand can be – handy.

If you happen to have the development module installed (which you should have) then the following path with flush the cache:

/devel/cache/clear

but also the following path lets you empty the cache manually:

/admin_menu/flush-cache

In my case this problem seemed to be a cache related problem. So emptying the cache helped. Luckily I found an easy fix for the problem over at drupal.org – so I didn’t have to empty the cache constantly. Here’s the details:

at the end of settings.php add this:

// admin toolbar fix
 $conf['admin_menu_cache_client'] = FALSE;

i found the quick fix for this problem over here: “Admin menu disappears (randomly), needs either cache to be emptied on every page or page refresh several times”
https://www.drupal.org/node/442560

and the fix was then right here:
https://www.drupal.org/node/442560#comment-2692220