Valérie Kudeljan 

Is your project in Trados Studio a file based project or a cloud project?
You can confirm this by looking at the type column when in the Project View

Lyds 

Hello Lydia,

Thank you for your question. It is a local project, not cloud-based. It contains multiple files spread out into multiple sub-folders. That is why a cloud-based project was not an option, as I understand subfolders are not currently handled by the cloud format.

Valérie Kudeljan 

Hoping this article was out of date, I did do some testing based on various Studio based projects linked to the Translation Engines in the Cloud. 
It is true that file based projects cant use batch tasks that rely on Translation Engines in the Clouds.
As you will note from the article linked, this is being addressed.

Lyds

Strange, as this exact same process was working just fine last month, and I was thrilled.

Let's hope the feature becomes available and stable in the coming months, as it seems odd that it doesn't work out of the box.