In my game have 2 levels but in first level Bg work in second level BG don't work, he stayed black.
Most likely you did something wrong
Seriously though, we could do with a little more information
I made a game, I exported it to Ludei with cacoonJS in the browser when I run normally works with the background. In the phone only the first level is the second level with background turns black background
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Yes, with such limited information ... all I can say is ...
You are likely doing something wrong.
What information would help?
I got it, the problem was in the picture have a very large resolution: p