AEM 6.4 Granite shows JS error _EditableUtils when authoring editable templates

[sardinchen]

We're running an instance on AEM 6.4.6.0. The authoring interface does not load anymore when attempting to author editable templates. It shows the following JS error: TypeError: ns.ContentFrame._EditableUtils is undefined

Using the debugger, I can see that this function is affected, which seems to be Granite built-in:

ns.ContentFrame._EditableUtils.shouldFilterEditable = function (editable) {
    return !!editable
};

The problem occurs with and without minification. Any ideas?

[sunjot16]

What error do you see in error.log file when you try to reproduce the issue?

Did it start happening recently, or it's been observed since the beginning?

[sardinchen]

Thank you for replying @sunjot16. I could solve the issue, it was a faulty overlay (but I cannot delete the question...)