Sheets/reports within a Collection that have managed references to sources outside of the Collection will fail with errors for those formula cells.
What's the point of Collections if you can't pull source data into it from outside the Collection in Workspaces you don't want people to have access to? I didn't have this issue with WorkApps…
It would be nice to be able to use Collections to provide curated views and access control without having these columns error out for people who don't have access to those sources within the managed reference.