I have created a simple game, I use the standard roch, and bush with starter materials on.
I also have a few custom materials and meshes in the game.
When i run a standalone/packaged game, all the foliage actors exports without materials on them, as in they appear with basic grey colours on them. When in editor, or PIE they appear as they should.
All other meshes and materials appear as they should, it is only the foliaged materials that has this problem.
So I would check to make sure you are adding the directory of your custom materials to your packaged project. I would also try packaging using the ‘Full Rebuild’ option under Development.
Can you reproduce this in a new blank project so I can test on my end?
Please provide any steps as clear and as simple as possible for me to reproduce this issue. This way we can narrow down the cause of the issue and any other outer lying issues.