Write to data store

Hi, I have a variable of type document and another of data entity type where I need to store the documents, in all the process models I have this:

but in just one case the documentId is not filled hence I am getting an error when trying to use the cmcDocument variable. In database it is inserted as expected:

the instance: 

I don't know what can be the problem as in other process models it is working and there is no difference between those processes