Hi!
I was testing the beta version 5.0b26 and experienced a major issue with the background image. You could easily specify a background image for your project which was then instantly displayed in the preview pane, but it was not rendered in the exported media file (tried with several export types). The background image is just not rendered. Specifying a background color instead works.
Furthermore, the project lost the reference to the background image very often, so it always prompted me about the missing file and where to find it. I only had to confirm the suggested location, because it was already the correct location. Only difference to the other images was that the background image was situated one level above the other images of the project in the file hierarchy. I’m not sure but I think I also tried to use an image from the same folder where the other images were stored.