Creator App on Mobile - Workflow "On Create / Edit - On Load" not triggered ?

Creator App on Mobile - Workflow "On Create / Edit - On Load" not triggered ?

Hi Everyone,

I built an application to track assets, which is used both at the office (desktop) an in the field by technicians (mobile app). 
In the field, technicians open an existing form and add rows to a subform at some point. One field they have to enter is a dropdown for which the contents are loaded through a workflow triggered on and "On Create/Edit - On Load". This works fine on desktop, but on mobile the dropdown is always empty, which makes the app useless in this case (other workflows depend on this field).

We verified that the apps are up to date, tried on iOS and Android, browsed the forum to find a solution... But for now nothing. 

Any idea how I could ensure my workflow triggers on the mobile app ? 

N.B.: other workflows "On Create/Edit-On Load" do trigger, even within subforms.

Many thanks for your help.
Kind regards