node_modules directory then doing a
meteor npm install should clean things up.
BUT, be aware that NPM will generally install the latest compatible versions of all modules, so there is a chance that it downloaded newer packages that aren’t as compatible as expected.
You can use
meteor npm list to list the versions installed, and
meteor npm outdated to see which if any are out of date and have updates available (without installing them!).
Maybe you should compare the versions listed in your package.json against the installed versions, or do a comparison with the versions installed on a different machine where they are working well.
To install a specific version (to go back a version or two) add a version number to the install command line, e.g.:
meteor npm install email@example.com
If it does turn out to be that a newer npm package version is the issue you can change your package.json to require a specific version instead of the default ‘compatible with’ by removing the hat symbol, e.g. changing:
< "babel-runtime": "^6.20.0",
> "babel-runtime": "6.20.0",
Other than that, all I can suggest is to debug the specific issues to try to narrow down what the root cause is.