Failed to acquire the lock - Status 409

[DanBarack-CLK]

I am trying to create a workflow that waits for external events. I implemented it with FORK and WAIT tasks. The WAIT task are triggered by API calls.

My workflow looks like this:

FORK
  |--- my_wait_task_ref-1 (WAIT task)
  |--- my_wait_task_ref-2 (WAIT task)
JOIN (on my_wait_task_ref-1, my_wait_task_ref-2)

When I am trying to update one of the wait tasks to COMPLETED I get the error

{
  "status": 409,
  "message": "Workflow lock could not be acquired",
  "instance": "f4bb06980a08",
  "retryable": false
}

I work on local development machine with Docker compose that includes conductor:server, elasticsearch and redis:6.2.3-alpine.

It seems that there is a limitation with parallel WAIT tasks . What is the correct way to wait for several events ?