When opening the editor, the first bake (first in sense of first time we click on generate after opening the editor, not specifically the first time we bake the scene) with GPULM and Progressive updates doesn't show any update. The second bake, could be trigger by a clear lighting and reclick on Generate lighting OR change some lighting and reclick on Generate does show some progressive updates.

I could reproduce it on several projects, even the some simple ones, (the one attached to this bug).

Reproduces only with GPULM.
Reproduces on latest trunk (2021.2.0a1)
Reproduces on 2020.2.0b2

Doesn't reproduce on 2020.1.0a25