the problem :
When removing the file via a click on 'Remove' and submitting the form, the target document still contains the id of the removed file.
my solution :
As a quick fix, I have overwritten the fileId helper as follows
Template.afFileUpload.helpers({
[...]
fileId() {
return Template.instance().fileId.get() /* || this.value */; // <== commenting this part solves the issue
},
[...]
});