Recurring Flagged Email Created a Mess

I have been using MS To-Do for a while and one flagged email is creating a mess that makes To-Do virtually unusable.

I made the flagged email recurring and now have 27,000 copies (no I'm not kidding) in my Flagged Email box in To-Do.  It is not dealing well with this.

I've tried deleting them, but To-Do isn't dealing with that well either.  Any ideas about how to fix this problem?

Thanks.