@BrianMcAuslan1,
I understand your frustration. You're in good company!
Thanks for reporting this to your local support group.
The "duplicating legend item" issue that has been resolved for Pro 3.4 (and hopefully available with 3.3.2) was introduced at 3.3 (released this past spring). That you've been seeing an issue as far back as 9/21 leads me to believe that your bug is not the same as BUG-000167906 A legend item element gets duplicated when copying a layer from a map frame on one layout to another map frame on another layout.
We might get lucky and the fix for the scenarios outlined in BUG-000167906 also addresses similar scenarios we did not know about and specifically test against.
Do you know if your local support reported this to Esri Support? If so, is there a bug number or incident number for reference you pass along to me? It would be good to get your scenarios and see if the fix for BUG-000167906 will also work for your scenarios.
Tom