I found a (temporary) solution for this problem.
The primary cause is that WordPress 5.5 changed the versions of jQuery and the way it is supported.
The WordPress Team made a plugin called “Enable jQuery Migrate Helper” that solves this problem. It basically enables an older version of jQuery. You can download the plugin from https://www.ads-software.com/plugins/enable-jquery-migrate-helper/ Download and enable the plugin and it will work.
The whole story on jQuery in WordPress on https://wptavern.com/major-jquery-changes-on-the-way-for-wordpress-5-5-and-beyond
The future plugin should be changed to a newer jQuery version.
Hope this will solve your problems.
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This reply was modified 4 years, 2 months ago by jaapwiering.