Insert Html Snippet prevents TinyMCE from loading

All of a sudden Insert Html Snippet prevents the TinyMCE editor from loading. It happens with both TinyMCE Advanced and the regular WP editor.

I notice I’m not the only one with this problem. It however has nothing to do with the WP version. I upgraded to 4.2.3 one week ago and all went well until yesterday. Also, the problem occurs in Chrome, not in FireFox.

The errors I see in the console are the following:

1. Refused to execute script from ‘/index.php?wp_ihs=editor_plugin_js&wp-mce-4109-20150505’ because its MIME type (‘text/html’) is not executable, and strict MIME type checking is enabled.
>> post.php?post=9&action=edit:1

2. Failed to load: /index.php?wp_ihs=editor_plugin_js
>> tinymce.min.js?ver=4109-20150505:4

One thing I did change is caching. I’m using W3 Total Cache with XCache now. Earlier I had only WP Super Cache. Deactivating W3TC does not help though. I did not try removing XCache.

https://wordpress.org/plugins/insert-html-snippet/