When using Nintex workflow tasks and using Lazy approval emails can take a long time to send.
- As an additional symptom you may receive an “access denied” when approving or denying a task.
Please ensure you have granted Nintex Workflow access to User profile services in the O365 site.
Go to your Site -> List -> Nintex workflow gallery - > *top-right* cog icon -> "Administration Settings" -> Grant Access to Workflow -> Trust the app
You should not need to republish any current workflows.