Hi Nigel,
I'm waiting for a reply from SuperPWA support.
If the reply doesn't arrive by the weekend, I will deactivate the Super PWA plugin.
If I will deactivate it, all works fine immediately or I need to do something?
Even when you delete the plugin, any browser which visited the site while that plugin was activate will have the service worker JavaScript code installed.
If you open the browser dev tools while in the back end of your site, navigate to the Storage tab (screenshot), then expand each of the storage options in the left and delete everything within. That should eliminate what was installed in your browser storage by the plugin. (You'll need to log back in to your site.)
Also, in the Application tab you'll find sections for Service Workers and Manifests. Delete these, too.
If you use more than one browser, or more than one computer, for editing the site back end, you'll need to repeat this for each of them.