Hi @qopwer12
Thank you for your posting.
I've made a test which has run successfully.
You can use the template in your link, just change the recurrence to 1 month and add two rows in the condition:
In my test, I suppose the trigger runs at the first day of every month and the flow will get all the tasks completed in the past month.


The dynamic content 'value Percent Complete' is chosen from 'List tasks'.
The expression used:
formatDateTime(items('Iterate_through_tasks')?['completedDateTime'],'MM')
formatDateTime(subtractFromTime(utcNow(),1,'Month'),'MM')
The last row in the condition is used to check whether the month of task completed date is equal to the past month.
For more info about the functions formatDateTime(), items(), subtractFromTime(), utcNow():
Reference guide for functions in expressions - Azure Logic Apps | Microsoft Docs
Reference guide for functions in expressions - Azure Logic Apps | Microsoft Docs
Reference guide for functions in expressions - Azure Logic Apps | Microsoft Docs
Reference guide for functions in expressions - Azure Logic Apps | Microsoft Docs
The tasks completed in my all 4 buckets are:

The result of the flow is:

If you still have the problem, please feel free to let me know.
Best Regards,
Community Support Team _ Kira Xie
If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.