I’m using the particles from the shooter template in my project. They look and act fine when I run in viewport or a second window, but when the game is packaged or ran as a standalone game, they render as tjhe default material checkerboard squares instead.
What happened was that after migrating these from the shooter example project to my project, I moved them within my own directory for organization. This ended up breaking a lot of textures, but for whatever reason, it still retained that the textures were in the old directory location, so they worked fine unpackaged/standalone game. Closing and reopening the editor came up with a ton of error messages for it. Seems like Unreal did not auto update the locations for whatever reason as it normally does.