When running a Plugin from a Clean Installation it seems to attempt to resolve it's dependencies too early.
Resulting in dependencies getting resolved to null before Assembly Generation completes for the first time.
Marking as Optional Dependency does not help.
Leveraging Late Dependency usage does not help.
Dependencies get resolved properly from there on out after restarting the game.

Forcing all loaded Assemblies to re-resolve their dependencies after Assembly Generation would probably be a viable solution.