This behavior also seems to be a bug in the select-contact functionality (specifically related to the handling of pre-populated values). I have logged db-object-widget not re-triggered when field becomes relevant · Issue #8653 · medic/cht-core · GitHub
In the cases were you are loading a pre-populated contact value that should not be editable by the user, I think the recommended approach for now would be to just do that in a group that is always relevant (but then maybe display the data and related questions in a different group that can start as non-relevant).