CM registration does not work with Joomla 3.8.3

We have a web site which uses the community builder user registration (CB configuration: Registration: Allow User Registration= Yes, Independent of CMS "allow registration")

The user registration worked with Joomla 3.7.5. After a while we had some problems to upgrade to Joomla 2.8.1 but finally we managed to upgrade it to 3.8.3. At the same time we have upgraded the multiple plugins of community builder like auto actions, activity, groupjive etc.

We tried to register a user in registration form but nothing happened, pressing a button does not do anything. We tried with Joomla 3.8.2 with the same results.

Switch to default Joomla protostar template, clear Joomla cache, then retry. If clicking the button does absolutely nothing it's likely a JS error blocking the form validation which submits the form after validating. If issue persists with default template press F12 to open your browsers console, select the console tab, then refresh the page. Now see if there's any errors present in the console tab (they'll be in red). If none click the submit button and see if any are there now.