Warning – Page may not be loaded properly – Error After updating WordPress

I have just updated WordPress from 5.2 to 5.7

In 5.2 Adinserter was working perfectly. Since updating when I view the plugin backend I can’t access any of my ads. I get the warning message – Page may not be loaded properly

See screenshot – https://prnt.sc/11vcx6u

I’m not running any adblockers, as mentioned everything was working perfectly in WordPress 5.2.