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It would also be great if users in the group could see the tasks under My Tasks.
It would be impractical to a modify the WF everytime some joins/leaves the Sharepoint site.
We use multiple Sharepoint online groups to easily manager task assignment to teams of users.
looks like NWC is back on the shelf until there is an answer to this...
Additionally, the action should be able to canceled by "Nintex Workflow Cloud - Complete a task". As I explained in another idea;
https://nintex.uservoice.com/forums/430063-5-nintex-workflow-cloud/suggestions/44307258-enable-action-nintex-workflow-cloud-get-tasks 
as of now, Nintex Workflow Cloud connector actions can't process any tasks generated by "Assign a task to multiple users" action. It could be a problem in a case where an operator wants to terminate unanswered tasks without stopping a workflow instance.
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update Dec.21th
By calling NWC API task v2 from Call Web Service action, I could query tasks generated by "Assign a task to multiple users".