"I edited the group to September 1st and I am still getting August 1st.  There doesn't seem to be a way to remove the history without deleting the group."

Don't Delete the Group. Open that List and look at the little handles on the left = This is a Basic List Management task.

Make  a New Group. Click and drag them into the New Group. Now delete your Old Group.

"I tried every option under Edit Group and I still get the pop up...."add to my reminders list" - still get the pop up, "do not remind me" - still get the pop up, "automate transaction entry" with "09/01/2018" as the "next date" and still get the pop up..."

Things get corrupt, especially across years of updates. Make a New Group and slide everything there.