ping @Hackwar

Do we have a way to see this error in core components? Looking at this, I'm unsure if this is an issue with the router. Shouldn't the redirect URL is built in getRedirectToItemAppend method of the controller like how we do in Joomla core, like this https://github.com/joomla/joomla-cms/blob/4.0-dev/components/com_content/src/Controller/ArticleController.php#L284 ?

Note: This issue occur only when you have a menu item for the form page, with the URL in menu something like this - index.php?option=com_communitysurveys&view=form&layout=edit

Now, in my controller, getRedirectToItemAppend returns the value &layout=edit&Itemid=484&return=aHR0cDovL2xvY2FsaG9zdC9qMy8=

If I add var_dump in the FormController class just before the edit screen redirect set, the redirect value prints null. So the redirect value was not yet set.

Which is then passed to JRoute::_ in the FormController class

// Redirect to the edit screen.
$this->setRedirect(
	\JRoute::_(
		'index.php?option=' . $this->option . '&view=' . $this->view_item
		. $this->getRedirectToItemAppend(), false
	)
);

After this, if I print protected redirect value it shows like this

protected 'redirect' => string '/index.php?option=com_communitysurveys&view=form&layout=edit&Itemid[0]=2604&return=aHR0cDovL2xvY2FsaG9zdC9qMy8=

So definetely, this is not an issue with the getRedirectToItemAppend. JRoute is changing the ItemId to array when the menu item exists.

Following rules are added in the router file.

$this->attachRule(new JComponentRouterRulesMenu($this));
$this->attachRule(new JComponentRouterRulesStandard($this));
$this->attachRule(new JComponentRouterRulesNomenu($this));

Hope this helps.

Please confirm this is Joomla 3 ?

Yes, Joomla 3 latest version as on date.

Please note that I can reproduce this issue in Joomla 4 as well, precisely all Joomla3/4 versions using the new Joomla router.
P.S. If there is no menu item created, the issue won't occur.

I'm guessing you have defined the view configuration for your form view to take an ID. Remove that and the error should go away

I looked up the code again and yes, that is indeed the problem. This is not a bug on Joomlas end. Closing this one.