Hi,
I’m having a similar issue with the HDRBackdrop in 5.5.1. I do have Lumen and Hit lighting for reflections enabled, as well as Screen Traces option on.
It’s been quite inconsistent within the same projects - it usually works in the beginning, but it stops working randomly later on. I can’t say that I’m doing something specific that makes it break, but it does.
Once thing I’ve done today is to change the mesh type from Dome to EnviroBox soft - the reflections came back when I did this, but then they went away when I re-opened the same project.
If anyone has any insight into this, it would be appreciated, as the randomness of it makes it hard to figure out what’s going on.