To be able to query for read/starred items in a project, the corresponding configuration option needs to contain the project IDs. This is done as a performance optimisation, and enabling this option will have a slight performance impact.
# For caching reasons the read/starred flags aggregations are now disabled
# by default. You can enable it by configuring a project id here.
# Mulitple ids can be provided by comma-separating them.
enable_flags_for_project_ids = XW1vSnxiRp-O4XCvJrA5Jg