5.7.x cache problem
This behavior does not seem to have any logical pattern. Sometimes the edit toolbar is visible on a certain page, sometimes not. On most pages it seems to be visible most of the time, but some pages are problematic. All the pages should have exactly the same, global settings.
When I turn the cache off, I do not face this problem anymore.
If it has, try switching it off in 'Control Panel'
Any other suggestions? :)