To my knowledge, CorDapp Custom Serializers have never worked properly with Driver. However, support was added to Driver's "out-of-process" nodes as part of the DJVM integration work in Corda 4.4.
which uses "out-of-process" nodes (i.e. runInProcess = false).
If you change this test so that runInProcess = true then it will fail. See also .
investigate whether Driver can also support Custom Serializers for "in process" nodes.