Accessing Library through Seahub > Departments throws "permission denied" error

When accessing a Library through:
System Admin > Departments > “Name of Department” > Libraries > “Name of Library”
the Seahub GUI throws an error “permission denied. Please try login again.”.
See screenshot below.
Any ideas on why this happens and how to resolve it?
A quick look in the seahub.log does not give any clues - no errors come up in there.