I don't see anything in the instance rules about bots: https://mastodon.world/about (yes, that's a mastodon instance, it's linked from our instance sidebar... the admins are the same and that's where they post the rules for both).

The backend versions are real close. So it doesn't FEEL like it should be an API issue. But lemmy.world is a heavily tuned instance that often runs pre-release code that hasn't yet been merged upstream in order to deal with its large scale. It's possible some API behaves differently, but to get meaningful help I think it's likely you'll have to debug it down to a particular API call and post the whole request/response from the two servers (omitting credentials).

Separate from your issue, is your code open-source? I profile stalked you to see what you might be doing and saw your test posts look like a sports community. I know the mods of !formula1@lemmy.ml are on the prowl for helper bots for raceday threads and such so I'm trying to keep an eye on what's available.