Widget backend not working properly

Hi,

I was trying to edit a text widget, but I wasn’t able to add text or anything to it. It displays only a frame with the title of the widget “Text” and the “{save}” button is greyed out.

When I run the inspector on my web browser, I get the following errors:

[Error] TypeError: undefined is not an object (evaluating 'wp.mediaWidgets.init')
	Global Code (widgets.php:86)
[Error] TypeError: undefined is not an object (evaluating 'wp.mediaWidgets.modelConstructors')
	Global Code (widgets.php:90)
[Error] TypeError: undefined is not an object (evaluating 'wp.mediaWidgets.modelConstructors')
	Global Code (widgets.php:98)
[Error] TypeError: undefined is not an object (evaluating 'wp.mediaWidgets.modelConstructors')
	Global Code (widgets.php:106)
[Error] TypeError: undefined is not an object (evaluating 'wp.mediaWidgets.modelConstructors')
	Global Code (widgets.php:114)
[Error] TypeError: undefined is not an object (evaluating 'wp.textWidgets.idBases')
	Global Code (widgets.php:124)
[Error] TypeError: undefined is not an object (evaluating 'wp.codeEditor.defaultSettings')
	Global Code (widgets.php:130)
[Error] TypeError: undefined is not an object (evaluating 'wp.customHtmlWidgets.idBases')
	Global Code (widgets.php:137)
[Error] ReferenceError: Can't find variable: wpWidgets
	Global Code (widgets.php:6332)

If I click on one of the “widgets.php”, there’s the following code:

<script type='text/javascript'>
wpWidgets.l10n = {"save":"Save","saved":"Saved","saveAlert":"The changes you made will be lost if you navigate away from this page."};
</script>

I have tried to re-upload the “wp-admin” folder a couple times, it is not fixed.

I deactivated YOAST SEO Plugin which made the “Customize” live preview return blank.

Is there a way to fix this?

Thanks in advance for your help.

The page I need help with: [log in to see the link]