Since the new update I get Child not found on container errors, how to fix this?

FOr multiple projects I currently get the following error
As it happens in multiple files and even if I rebuilt it I cannot fix it I am wodnering how you can find the cause of this error and how to solve this?

Could someone please assist?

Hi @Marco_Willigenburg ,

Does this error happen when you Run the Project ? Is it also the same when you Debug ?

Also try creating a separate sequence (Test - Message Box) and check if that individual file executes.

Let us know your findings/feedback.

it happens both, but also activities are not seen anymore even if they were jsut adjusted.

Does it help if you update the Excel activity package to the latest version?