Unwanted re-executions under heavy load / slow DB performance

**Describe the bug**
In a slow system, job lock time may expire and lead to multiple executions.

We noticed in a system with slow DB performance that they hit FlowableOptimisticLockingExceptions - which caused re-executions, which we then prevented using the async handler number of retries = 0.

We then noticed re-executions and FlowableOptimisticLockingExceptions and deducted that slow DB performance lead to them.

**Expected behavior**
No re-execution of jobs should happen if lock owner still alive.

**Code**
No code - I tried with a simple model with 3 service tasks: task1(async)-task2-task3(async), and I changed the lock exp time to the past while stopping task2 via debugger.

**Additional context**
Flowable 6.2.0 in Spring boot - with Oracle 11g. I reproduced the issue in a H2 (standalone, tcp) and a unit test.