That's frustrating! I'm sorry that the plugin didn't correctly handle spritesheets right out of the box for your game jam project.
Thank you so much for taking the time to report this specific issue and, even more importantly, for providing the detail about the UV calculations you used to fix it. This kind of specific feedback is incredibly valuable for improving the asset.
I will improve the code based on your findings and make the code work with spritesheets for future updates.