IBM App Connect Enterprise v12 - groupId created by GroupScatter node is not unique

Question

I have group scatter, group gather and group complete nodes in my flow. When I call my flow multiple times in parallel sometimes pair of the flows fail because groupId created in group scatter is the same for them. GroupId should be unique according to IBM manual. It looks like its seemingly randomly.

I checked group related times from in LocalEnvironment. GroupCommitTime for one of them is lower than GroupCreationTime for the other one.

I also tried several load tests with 10 requests, half of load tests were with zero fails, half of them with 1 duplicit groupId and one load test was with 2 duplicities. I tried 2 load tests with 100 requests, one was with 0 duplicities, 1 with 4 duplicities.

It truly looks like its random. Is there any known bug, do you have any idea what I could try or do you have any explanation for this behaviour?

Im using IBM ACE 12.0.12.0, openshift and Red Hat Enterprise Linux 8.9