Thanks pchamorro for bringing some light.
I have a lot of ubuntu servers (from 12.04 to the latest 20.04.1). Most of the appear correctly identified in the main page. This handfull of servers (5 exactly) don't.
They are not of the same version (18.04, 20.04 and older), the IT staff changed the agent on the affected computers and nothing changed (still displays ubuntu).
How is the OSName obtained? I'm thinking that something might be changed manually on those computers.