at some point it looks like you had a Struct and got deleted. i have read theres a bug about broken references. Whenever i have this kind of issues:
- Delete Intermediate folder
- Delete Saved folder
- Delete Binaries folder
- Inside your project, right click on Content (inside Content Browser), “Fix Up Redirections in Folder”.
ofc, if in doubt, backup your project first. also, have you tried building a sample template?