This past week I had an issue of some of my Nintex workflows just not running for some reason. They would get to a certain point and just decide not to complete the next step.
Recently i added a new application server into my farm and I did not realize that in order for these workflows to run correctly they needed to have the Microsoft SharePoint Foundation Workflow Timer Service only running on the web front ends (web servers), since that is where the Nintex service actually runs.
So if you are running Nintex Workflow in your farm and you have a multi-tier farm for your SharePoint setup, go to central admin and check your service settings like below:
To be clear once more, this Should be running on your web servers if you have Nintex workflow, but should not be running on your application servers.
I found this out the hard way after having to contact Nintex support one day.
Hope this helps others,