let me try again...
Ah, there it is actually an unrelated problem
silverstripe/fulltextsearchbut there's still some reference to it somewhere after dev/build?flush=all
[Emergency] Uncaught SilverStripe\Core\Injector\InjectorNotFoundException: ReflectionException: Class SilverStripe\FullTextSearch\Search\Extensions\SearchUpdater_ObjectHandler does not exist in /var/www/html/vendor/silverstripe/framework/src/Core/Injector/InjectionCreator.php:17
Had to restart the Apache dev server
Found another one, I think it is an Elemental bug. When I click to change a block, the panel redirects to the SiteTree page again. I'll issue it in Elemental-subsites.
try elemental, but mention you are also using subsites and the elemental subsites module