Layer update fails to give cloud username

I have a layer of buildings which has data in it.
One of the attribute is username which should save the cloud username if there is update in the particular building point.
But NULL is coming instead of cloud username. "APPLY default has been checked in qgis attribute form field’
What should be done.

However this is not the case if new building point is added. username does come whenever a new building point is added.


Imported from GitHub discussion by @MonikaShah on 2022-09-20T10:23:50Z