My browser / operating system: Windows NT 10.0, Chrome 131.0.0.0, No Flash version detected I was making a project for christmas, for some reason every sprites costumes had a ton of copy and pasted versions of itself stacked onto each other ( basically, if i created a box then tried to drag it somewhere in the costume editor, there would be like, 1000 more boxes under it.). Pretty annoying, i noticed it an entire I think 3 hours into making the project and had to delete all my work.

yep I had that too one time
try restarting the page

I shall try that if i ever encounter the same unorthadox error