After much headache, I figured out what the issue was for me. I was importing a library that we build ourselves, and that library had a different version for the @angular packages than the root project since we upgraded them both a few weeks apart. After ensuring the packages the two projects shared under were the same version (did so for non-angular packages), this error went away for me. When they were different versions, they didn't share the same context anymore, disallowing for proper injection.