Hi I'am also having sometimes some constraints violation when mixing batch insert and update even with 5.2.12.
With 50 as batch size and 40*1000 entities saved with a Spring Data save(List<> of entity).
The current workaround is to do insert first and then updates in a second time, without mixing creation and update in the save(List<> of entity) method.

I'll try to find time to create the test case.