From Pega 7.1.7, merge/batch is introduced as default mode for saving (deferred/immediate) instances instead of INSERT and UPDATE.
In the same transaction, the instances could be grouped into multiple batches by prepared statements. The process does not necessarily maintain deterministic orders for instances. This could potentially violate execution orders wherever a mandatory order is needed (for example, foreign key constraints).
This issue is resolved through the following local change:(SR-9399)
Disable merge/batch by change the following prconfig settings. This requires to restart PRPC.