Curious if anyone else has noticed this before contacting support - we have found that disabling the 'inform original participants' escalation option for the assign a task action does not appear to stick. We have not confirmed for start a task process but suspect the same behavior as well.
To reproduce - after closing/reopening a workflow that includes an assign a task action with this option unchecked - reopened the assign a task action's config dialog shows that this option has been re-enabled. We did, however, confirm that the actions behavior to send or not send this message behaves as intended until the workflow is reopened, that action opened to check its configuration, and then the workflow is republished.
We've experienced this in multiple O365 environments but would love to hear from our fellow Nintex users as well.