Yes, it seems that shotcut freezes every time when you try to add % in an image name. It’s a bit of a glitch, but don’t worry, there’s a simple fix. Just rename the image file and remove this % character from it’s name. That should solve the freezing problem. (but do not break the image format)
You already have reported it and the developers are aware of your report. The person who first replied to you is just some person who just joined the forum. He’s not a developer of Shotcut.