This anomaly occurred even with read concern snapshot and write concern majority
3.5: In this case, a test running with read concern snapshot and write concern majority executed a trio of transactions with the following dependency graph
3.6: Worse yet, transactions running with the strongest isolation levels can exhibit G1c: cyclic information flow.
3.7: It’s even possible for a single transaction to observe its own future effects. In this test run, four transactions, all executed at read concern snapshot and write concern majority, append 1, 2, 3, and 4 to key 586—but the transaction which wrote 1 observed [1 2 3 4] before it appended 1.
Like... if you had read any of these sections--or even their very first sentences--you wouldn't be in this position. They're also summarized both in the abstract and discussion sections, in case you skipped the results.
4.0: Finally, even with the strongest levels of read and write concern for both single-document and transactional operations, we observed cases of G-single (read skew), G1c (cyclic information flow), duplicated writes, and a sort of retrocausal internal consistency anomaly: within a single transaction, reads could observe that transaction’s own writes from the future. MongoDB appears to allow transactions to both observe and not observe prior transactions, and to observe one another’s writes. A single write could be applied multiple times, suggesting an error in MongoDB’s automatic retry mechanism. All of these behaviors are incompatible with MongoDB’s claims of snapshot isolation.
It's OK to stop digging now!