Describe the bug
When multiple exclusive external worker jobs with the same topic belonging to the same process instance are available for acquiring, no external worker jobs will be acquired.
This is caused by the AcquireExternalWorkerJobsCmd which will try to lock the same process instance for each external worker job.

Locking the process instance for the first external worker job will succeed, but the second one will cause a FlowableOptimisticLockingException.
The FlowableOptimisticLockingException will rollback the acquire process and after a couple of retries no external worker jobs will be acquired.

Expected behavior
When multiple exclusive external worker jobs with the same topic belonging to the same process instance are available for acquiring, non exclusive external worker jobs and exclusive worker jobs (one per process instance) will be acquired.

Code

Additional context
Flowable 6.7.3-SNAPSHOT