According to your description, I have started a flow from the template “Create planner tasks for flagged emails in Office 365” you mentioned.
However, the issue that the tasks get duplicated multiple times doesn’t occur on my side.
The flow will be triggered only one time when an email is flagged and one task will be created in Planner.
Could you try again with it?
Please feel free post back if you are still having the issue.
i got the same issue,
whenever i answer or receive a followup of the same mail conversation as the flagged e-mail, i got another task created .
seems like answering or receiving a mail with the same subject is similar as flagging a new email .
i suppose that @j0s03w8 is referring to this issue,