Good day, @indekchiropracti.
Thanks for coming to the Community for help. I'm here to share some information about printing checks in QuickBooks Online.
We have not received any reports similar to this. There currently isn't an option in QuickBooks that would allow duplicate printing.
You need to verify the printer setting. It's possible that the Copies field shows 2 instead of 1. I'm adding a screenshot for visual reference:
Here are articles that tackle more about the process of printing checks within QuickBooks Online:
That should answer your question for today. Reach out to me if you need additional assistance, I'm more than happy to help. Cheering you to continued success!