if you're using MV then most likely you have deployed your game into your working folder, and now every playtest redirects you to the deployed version while the editor accesses the working version.
If you have MV and if your working project directory contains a www folder, then you need to delete the www folder there and replace the damaged packages.json with the same file from a newly created project.
EDIT:
The OP just thanked me in an old post where I gave the same instructions, so this is most likely the same