TYPO3 Core

Confirmed & caused by https://review.typo3.org/c/Packages/TYPO3.CMS/+/68714/9/typo3/sysext/backend/Classes/Controller/EditDocumentController.php#416

Previously the response did contain HTML and corresponding markup to trigger notifications.
With having an HTTP GET redirect in place, this does not work anymore and needs a different concept/approach.

Notifications are triggered by \TYPO3\CMS\Redirects\Service\SlugService::sendNotification using

        GeneralUtility::makeInstance(PageRenderer::class)->loadRequireJsModule(
            'TYPO3/CMS/Backend/BroadcastService',
            sprintf('function(service) { service.post(%s); }', json_encode($data))
        );

Patch set 1 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/71410

Applied in changeset 629a43571939c1fa93f30bdcff951e75af144110.