I had the same problem, I just run the following command and it worked after without any error.
npm cache verify
If it does not, try manually deleting the node_modules folder and reinstalling the modules with npm install.
rm -rf node_modules
npm install
On npm > 6, you can also run npm ci, which also deletes the node_modules folder and reinstall packages after.
Edit As other answers suggested, you may need to restartng serve if the above steps do not work (but they normally do)