In this case, the customer has a balanced workflow 8.6 environment (2 nodes) and developed and published many different workflow projects. Some of these projects are designed to run for hours without human intervention. The issue seen is that some processes just stop running and do not finish. No errors in the logs are noted when this happens.
The behavior described occurs sporadically.
Application Pools in IIS recycled and caused a disruption in the workflow process
Release : 8.6
The customer created new App Pools in IIS on the Workflow Server and adjusted the recycling to occur off-house when processes are not running.