Scheduled Workflows Run Multiple Times

I've tried suggested resolution.
It did not help.

Here is our situation.
Workflow, scheduled run once a day.
Schedule settings:

Schedule end: Indefinite

It takes about 6 minutes for this workflow to complete.
This workflow does not have any pauses or waiting for anything to change:
only runs SQL query, collects data to build a report and sends emails.

Farm settings
1. Nintex Workflow Scheduler job is defined only once.
2. Nintex Workflow Scheduler: Runs every 5 minutes
3. The job is scheduled to run on 3 WFEs servers.

The scheduled workflow in question  runs twice every time. 
A simple workflow that only logs to history and stops, runs only one most of the time (9 times of 10) but sometimes still runs twice. 

I'm a little bit confused how scheduled jobs on 3 servers are able to synchronize to avoid duplicate runs.
Also, what happens when a scheduled workflow is still running and the next scheduled Nintex Workflow Scheduler job starts.

Any suggestions?
 

Hi Oleg,

This may be a SP Farm topology issue, or a conflict with how the Workflow Timer Job is trying to execute. I would suggest opening a support ticket and asking one of the engineers to review your farm topology to ensure that everything looks to be configured properly.

Thank you. Opened a support ticket.