changed Title to make clear its about 4.0

Issue confirmed.
@dgrammatiko
This happened when you modified the file to not use JQuery

I think I found the reason:
Joomla.showAssociationMessage = function() is adding the message for each Control group.

Can you set debug on (which will use the non minified js version) and then edit /media/com_associations/js/associations-edit.js
and replace the function with this code:

	Joomla.showAssociationMessage = function()
	{
		var controlGroup = document.querySelectorAll('#associations .control-group');

		for (var i = 0, l = controlGroup.length; i < l; i++) {
			controlGroup[i].style.display = 'none';
		}
		
		var associations = document.getElementById('associations');

		if (associations) {
			var html = document.createElement('div');
			html.classList.add('alert')
			html.classList.add('alert-info')
			html.id = 'associations-notice';
			html.innerHTML = Joomla.JText._('JGLOBAL_ASSOC_NOT_POSSIBLE');

			associations.insertAdjacentElement('afterbegin', html);
		}
	}

Yes, works! Great :)

Sorry there are no div ALERTS anymore, use joomla-alert Also we have a helper to create alerts...

That's another scope. Here it is a loop in the js over content languages. But thank you for the hint. @infograf768 would you make a PR?

@chmst NOPE. Please do not use Bootstrap classes that will not be included in J4. We already have our own components for alerts, use that!!!

@dgrammatiko
It was not my intention to make a PR. I just checked were the error was in the js (which still uses div alerts).
As I would not know how to code <joomla-alert in a js, please do PR yourself.

I have a patch ready using joomla-alert. Waiting for @dgrammatiko to correct a bug when compiling the js files.

@chmst
Closing as we have a PR
#21281