Gzip Compression got turned on
– Backend got messed up after turning on the Gzip Compression.
Solution using web inspector
This option doesn't work on most websites, and if you turned it on, then you could use Chrome, then right click on the Gzip compression text, and choose Inspect element.
Open up the code under it, until you find this:
Change the value to 0.
Click on the Console tab, write this code in the bottom, and press enter:
After the second refreshing the backend should show up properly.
Solution using PHP
Open up these two files:
You will find this in their beginning:
$this->_gzip = getNextend('gzip', 0);
You should change them to:
$this->_gzip = 0;
This way the code will think the gzip option is turned off and everything will load properly. Now you should go back to the Nextend settings and turn off Gzip compression, so if an update comes out, you would have this setting turned off.