IL2CPP is the active scripting backend, which we must use for platforms like Switch What I've found is that if scripts are located in a package with an assembly definition, any scene that is bundled inside of an asset bundle can not find a reference to any scripts in that package, if: The referenced script on this Behaviour (Game Object 'SomeObject') is missing! We get a heap of logs that scripts are missing when our scripts are added to assembly defintions and referenced in a scene which lives inside of an asset bundle: I'm in the process of submitting a reproduction project. I have however narrowed down the source of the issue which you all might find interesting because it could explain why some of you are having issues. any of the suggestions listed here were not helping my case. I found this thread due to a similar issue where any scenes I have which live in asset bundles were unable to find references to scripts which live in an assembly definition.