MongoDB had consistency issues when running as a distributed system, that's expected if you read Jepsen's reviews. Meanwhile, ParticleDB had bugs like this when running as a single node:

    root=> CREATE TABLE t
           (a int primary key, b int);
    root=> INSERT INTO t VALUES (4, 5), (5, 6);
    root=> SELECT * FROM t WHERE b = 4;
     a | b
    ---+---
     4 | 5