wp-mediaelement.min.js?ver=4.9.4:1 crashes, making the Widgets in customize.php unusable

[radual]

When accessing wp-admin/customize.php with a live preview, I am unable to add menu items or to switch between "Text/Visual" for the text widgets. At the first sight, it seems to be a problem with Javascript.

The console looks like having an error with the media gallery - Uncaught TypeError: Cannot read property 'indexOf' of null (see screenshot for details).

There is also a second error in the console - which does not seem related - but it may prove helpful: Error parsing header X-XSS-Protection: 1; mode=block; report=https://www.google.com/appserve/security-bugs/log/youtube: insecure reporting URL for secure page at character position 22. The default protections will be applied.

I have also disabled live preview with a die(), the situation is the same - which makes me think the error is more related to the way media gallery interprets some part of the content while rendering customize.php. Everything works smoothly for wp-admin/widgets.php (no Javascript errors).

There may be other sections that are affected, but I can confirm these two:

• Widgets > Footer X > Any text widgets: cannot switch between Visual and Text (stays blocked on Visual)
• Menu > Main Menu > Add items: items are not clickable (and the first one is not folded).

Browser: Chrome 64.0

[radual]

Javascript errors in console

[radual]

Adding menu items - not clickable

[audrasjb]

Hello and welcome on WordPress Trac @radual

I can't reproduce. Did it happens on a fresh new WP install and a bundled theme?

[radual]

Hi @audrasjb and thank you for the quick response.

The install is not fresh - it has been customized with widgets and plugins (which we disabled - but the problem kept persisting; we may try to disable them again just to make sure).

The theme that is being used is: ​https://catchthemes.com/themes/verity/

The media gallery is quite full of items - video, audio, images, so I couldn't track something specific to a certain item.

One of the widgets embeds a Youtube video, as you may see in the footer of ​https://lheuredupunch.com

[juhise]

@radual Would you mind trying with default theme? It might be theme issue, if it's still not working, try disabling plugins.