I think I've tracked it down to starman.
With only 1 worker, all works fine. I guess the second worker picks up the other request but not in the same DB transaction and doesn't see the update.
The question is now is it an internal starman cachine problem or am I doing something wrong with my database connection ?
My guess is that it's not only database because the session info is not pickup by the 2nd worker either so starman is doing something wrong, workers are not synchronized.
Is there any Starman-specific community I could ask ?