In my experience MongoDB has only given me problems (either performance or data loss). Most likely when someone wants so "solve" something with MongoDB, there is always a better technology to do it (Cassandra, ScyllaDB, S3!, PostgreSQL/JSONB). I could Imagine that their current implementation has a half modeled graph-like structure in MongoDB and migrating to something else (I am generally against Neo4J because of their horrible pricing tiers).