PartitionRouting SMT uses Java hash function which is not very suitable for things like spreading equally hashes over the hash space and consistent hashing. In small number of partitions it may result that all records end up in the same partition. Use better hash function (MurMur) for computing hash of the record fields.

See also https://debezium.zulipchat.com/#narrow/stream/348104-community-mysql/topic/Data.20is.20not.20distributed.20to.20different.20partitions