Are you reading the detailed reports prepared by the Jepsen audit team, or the press release? Jepsen audits are public.
The summary of the latest MongoDB report [1] follows,
"In this Jepsen report, we will verify that MongoDB 3.6.4’s sharded clusters offer comparable safety to non-sharded deployments. We’ll also discuss MongoDB’s new support for causal consistency (CC) in version 3.6.4 and 4.0.0-rc1, and show that sessions prevent anomalies so long as user stick to majority reads and writes. However, with MongoDB’s default consistency levels, CC sessions fail to provide the claimed invariants."
The summary of the latest MongoDB report [1] follows,
"In this Jepsen report, we will verify that MongoDB 3.6.4’s sharded clusters offer comparable safety to non-sharded deployments. We’ll also discuss MongoDB’s new support for causal consistency (CC) in version 3.6.4 and 4.0.0-rc1, and show that sessions prevent anomalies so long as user stick to majority reads and writes. However, with MongoDB’s default consistency levels, CC sessions fail to provide the claimed invariants."
[1] http://jepsen.io/analyses/mongodb-3-6-4