Update 5.3.3 auf 5.3.6: Choose Smaller Batch Size / Signature not valid

Hallo,

wir bekommen beim Auto-Update von 5.3.3 auf 5.3.6. folgenden Fehler im Backend: “An error occured. The server could not handle the request. Please choose a smaller batch size.”

Laut Log liegt es an einer fehlerhaften Signatur: 

Exception: Signature is not valid in /engine/Shopware/Plugins/Default/Backend/SwagUpdate/Components/UpdateCheck.php:142 Stack trace:
#0 /engine/Shopware/Plugins/Default/Backend/SwagUpdate/Components/UpdateCheck.php(111): ShopwarePlugins\SwagUpdate\Components\UpdateCheck->verifyBody(NULL, '\r\ncheckUpdate('5.3.3', Array)
#2 /engine/Shopware/Plugins/Default/Backend/SwagUpdate/Controllers/Backend/SwagUpdate.php(510): Shopware_Controllers_Backend_SwagUpdate->fetchUpdateVersion()
#3 /engine/Shopware/Plugins/Default/Backend/SwagUpdate/Controllers/Backend/SwagUpdate.php(346): Shopware_Controllers_Backend_SwagUpdate->getCachedVersion()
#4 /engine/Library/Enlight/Controller/Action.php(159): Shopware_Controllers_Backend_SwagUpdate->unpackAction()
#5 /engine/Library/Enlight/Controller/Dispatcher/Default.php(530): Enlight_Controller_Action->dispatch('unpackAction')
#6 /engine/Library/Enlight/Controller/Front.php(223): Enlight_Controller_Dispatcher_Default->dispatch(Object(Enlight_Controller_Request_RequestHttp), Object(Enlight_Controller_Response_ResponseHttp))
#7 /engine/Shopware/Kernel.php(189): Enlight_Controller_Front->dispatch()
#8 /vendor/symfony/http-kernel/HttpCache/HttpCache.php(491): Shopware\Kernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true)
#9 /engine/Shopware/Components/HttpCache/AppCache.php(268): Symfony\Component\HttpKernel\HttpCache\HttpCache->forward(Object(Symfony\Component\HttpFoundation\Request), true, NULL)
#10 /vendor/symfony/http-kernel/HttpCache/HttpCache.php(258): Shopware\Components\HttpCache\AppCache->forward(Object(Symfony\Component\HttpFoundation\Request), true)

In CheckUpdate wird der Body verifiziert. An der Stelle, wo es zum Fehler kommt sieht der Body so aus: 

503 Service Temporarily Unavailable

503 Service Temporarily Unavailable
nginx

Bedeutet das, dass der Update-Server nicht erreichbar ist?

Danke.