Travel back in time and undo your duplicate tasks' creation.
WARNING: This has only barely been tested, and although it did work as expected for the use case I wrote it for, the command it generates might be incorrect. Do read through the prompts carefully, and use this at your own risk!
pip install taskwarrior-timecrimes
Just run the following command in a shell:
You'll be presented with a list of dates having recent changes. After selecting the date that you'd like the duplicated recurrences to be deleted from, the command you can run to delete those tasks will be generated and printed to the console so you can run it yourself.