My issue is with date-fns 2.9.0 not installing. I went to Heroku and tried to npm install manually and it sits there until sometimes timing out after a long period of time.

Then sometimes it says

The authenticity of host 'http://github.com (140.82.113.3)' can't be established.acted to /app/server/node_modules/.staging/date-fns-74841dec (4779ms)
ED25519 key fingerprint is SHA256:+DiY3wvvV6TuJJhbpZisF/zLDA0zPMSvHdkr4UvCOqU.
This key is not known by any other names

I searched on Github here and the SHA256 data does match ok. So I wonder if this is a Heroku issue where known_hosts needs an additional entry?

I can't find the known_hosts on my dyno and not confident it would stick around even if I found it.

This could be a situation where npm install is going to github instead of a regular npm repository. I'm new and not sure. But I am loading a specific tag of a github repository right after date-fns which may be the real issue.