The sharded_backup_restore_chunk_migrations_while_backup.js test is trying to retrieve config.chunks documents by specifying the ns field in the filter.

As starting from v5.0 chunk entries are containing the collection UUID rather than the namespace, the following snippet must be adapted accordingly.

FROM:

mongos.getDB("config").chunks.find({ns: "test.continuous_writes_restored"})

TO:

mongos.getDB("config").chunks.find({uuid: collectionUUID})