ECA Action - Error message

Problem/Motivation

When using ECA → there is an Action named:

Webform Workflows Element -> Performance workflow transition on submissions

Steps to reproduce

When filling the configuration for this Action, an error message pops when saving the Model:

Error message
The subform and parent form must contain the #parents property, which must be an array. Try calling this method from a #process callback instead. 

No matter what is filled on the config form, we always get that message.

The Workflow select box is correctly filled with available workflows.