This problem is reported in #1077.. https://github.com/LLK/scratch-vm/issues/1077 I just removed Backspace (\b) from JSON and fixed it. I think it is the same problem of #4190. https://github.com/LLK/scratch-gui/issues/4190
The original project is written by @shu279. https://scratch.mit.edu/projects/194603038/