Dynamic forms according to the documentation generate Cannot find control with name ''

[sbeex]

I followed the following documentation:
https://angular.io/guide/dynamic-form

But then I figured out that it generates some errors when I load the data to create the forms from my REST API. (Some delay)

It seems I am not alone in this case:

https://stackoverflow.com/questions/48741641/dynamic-forms-angular-4-giving-error-cannot-find-control-with-namebrave-for-t

Could someone help me ? This is really blocking me since days I try to debug it but it's hard...