Hello, I’m also appearing to have the same issue after upgrading WordPress. However when I try to go to the widget section, I used the “Inspect Element” function on Google Chrome and there seems to be this error on the page.

Uncaught Error: Syntax error, unrecognized expression: a[rel=]

then it is followed by

Uncaught TypeError: Cannot read property 'hasClass' of undefinedload-scripts.php:258 (anonymous function)load-scripts.php:3 m.event.dispatchload-scripts.php:3 r.handleload-scripts.php:3 m.event.triggerload-scripts.php:8 e.event.triggerload-scripts.php:3 (anonymous function)load-scripts.php:2 m.extend.eachload-scripts.php:2 m.fn.m.eachload-scripts.php:3 m.fn.extend.triggerload-scripts.php:257 (anonymous function)load-scripts.php:2 jload-scripts.php:2 k.fireWithload-scripts.php:4 xload-scripts.php:4 send.b