It uses a lot of very specific terminology, but the linked pages like the one on "G-nonadjacent" do a lot to clear up what it all means. It is a lot of reading.
Essentially: The configuration claims "Snapshot Isolation", which means every transaction looks like it operates on a consistent snapshot of the entire database at its starting timestamp. All transactions starting after a transaction commits will see the changes made by the transaction. Jepsen finds that the snapshot a transaction sees doesn't always contain everything that was committed before its starting timestamp. Transactions A an B can both commit their changes, then transactions C and D can start with C only seeing the change made by A and D only seeing the change made by B.
Essentially: The configuration claims "Snapshot Isolation", which means every transaction looks like it operates on a consistent snapshot of the entire database at its starting timestamp. All transactions starting after a transaction commits will see the changes made by the transaction. Jepsen finds that the snapshot a transaction sees doesn't always contain everything that was committed before its starting timestamp. Transactions A an B can both commit their changes, then transactions C and D can start with C only seeing the change made by A and D only seeing the change made by B.