I came here to say this, but weirdly it just resolved itself… but it was a bug.
Using standard assets, GrassAndTreesBackground tiled image and Dino character I was creating a character, adding behaviours etc.
When I previewed my scene the background wasn’t showing but everything else worked fine.
The console was reporting that the Bg couldn’t be loaded because of CORS issues (I was using the web editor)… After Publishing my project - in the published version the bg was there… and THEN the Preview started working.
As I say. Just reporting this (there’s a glitch in there somewhere) … wonderful product btw.
I was unable to reproduce the issue on my side, the preview displayed both objects on my first attempt.
Can you confirm your operating system and browser, and let us know if you’re behind some network security system, company firewall or restricted network, perhaps?
It all works now… I think when assets are added they aren’t CORS until they’re published perhaps…
p.s This (my socks are blown off) is totally bloody amazing… as an old fart that yearns longingly for the glory days of HyperCard (a free authoring tool anyone can use) I think you may have cracked it… Well done!!!
Hi and welcome here 
