@drsebro Look, here, hopefully this illustrates what I'm talking about enough:
https://gist.github.com/Gargron/590b84aa766ce32c0bc7f004f27c52b1
Also, if you're not using Docker, you should know how to isolate your two servers from each other: Use different DB_NAME, use REDIS_NAMESPACE, and if using local filestorage for uploads, make sure they don't write to the same directory.
@Gargron look in the line 36 in both files. I have there one time mastodon and second time wartadon (I used wartadon as substitution for mastodon during the installation). What I probably not changed is the REDIS_NAMESPACE. I have to search for this.