As described in https://documentation.coremedia.com/cmcc-11/artifacts/2201/webhelp/frontend-en/content/ThemeConfigReference.html you can set the "defer" flag in your theme configuration to defer the execution of a JavaScript file. Due to a bug all CMJavaScript documents generated by the theme importer that were not meant to be deferred were configured in a way that caused the following HTML output:

<script .... defer="false"></script>

This can cause problems with other flags just like "async". To avoid any problems with other flags the "defer" flag is now once again omitted if not set to "true".

(CMS-21476)