You may try login and logout again to fix the problem but still nothing happens, but don't panic we will explain what is the source of problem.
Most of the time this is not a hacking issue or server side problem specifically if you are continuously updating WordPress core software, this problem may be caused by WordPress Cache plugins or Caching proxies.
There are many caching plugins for WordPress but we just focus on the most popular caching plugin: W3 total cache Plugin .
If you are not using both of the cache plugin and cache proxy then this article can not help you and you should find problem in other places.
Check W3 Total cache WordPress page caching plugin:
A brief information about w3 total cache plugin: Every time a visitor's web browser requests a WordPress page, WordPress engine runs a database query while processing PHP files and generates the requested page for the visitor but when you use Cache plugins like W3 total cache plugin it can help you speed up loading your WordPress based web pages by caching them and storing a copy of latest generated output of web pages in HTML format in disk space.
Then cached pages will be served to the visitors, this action stops WordPress engine to generate pages each time the page requested by a visitor and it can effectively reduce the server load and increase the web page load time speed.
Wrong configuration of w3 total cache plugin can be the cause of our admin bar showing problem because it may cached a page that you visited as admin when you logged in to admin area and it also may cause problems when logging in admin area because you will see cached pages instead of original processed page.
let's check the settings of this plugin step by step:
1. After logging in to admin area of your WordPress site go to the cache setting page through admin bar:
WordPress admin >> Performance >> Page Cache setting.
2. Tick the box for option "Don't cache pages for logged in users" as you can see in screenshot below:
|tick the box of option : Don't cache pages for logged in users ( click the image for larger view)|
3. Save the changes by clicking "Save all settings" button.
4. Clear the cache
If the problem caused by w3 total cache plugin then this solution can solve this issue.