Finder sidebar icon changed
In my Finder sidebar, the icon of a plain folder has changed. It looks like some document with a mouse pointer. No matter what I do, I can't change this icon in the sidebar back to normal. Every time I drag this specific folder (simple folder with audio files in it) back to the favorites sidebar, this strange icon appears.
In the screenshot the folder is circled in red. The folders above and below are displayed normally.
Any tips on how to return the icon to normal?
iMac, macOS High Sierra (10.13.4)