As Alexander Petrov noted

The fact that it is logging multiple statements in the log does not mean it is not doing the batching. Not every database supports SQL with one insert and many values.

I face the same issue with H2, where I see two SQL updates. But if I turn on the statistics via

spring.jpa.properties.hibernate.generate_statistics=true

I get for example this

1354250 nanoseconds spent executing 1 JDBC batches;