During some failover/rebalance scenarios, it could be the case that no master is responsible for the document. While this should not be the case, it is observed in scenarios where the client may still have an outdated config from somewhere.
This leads to RuntimExceptions raised, but reconfigure is never actively triggered. In QE tests, this manifests itself in errors during change and rebound.
While it should be elsewhere investigated how those -1 get in place, checking for this and triggering reconfigure is a safety net for running operations.