Sleeping shiny-app does not wake up and cannot restart

I have dispatched a shiny-app from R-Studio to shinyapps.io some time ago. Now, after the app has not been used for some time, it went into the state sleeping (as expected). However, it is not waking up when the url is called and when I try to manually restart it, I get the following error:

Unable to dispatch task for application=7397204 as there are 1 tasks already in progress. This is most likely a transient error. Please try again in a bit. If this error persists please contact support.

Any suggestions what else to try will be thankfully received.