I doubt I'd be encouraged if this happened for me so soon after joining. Even over 2 years in, it's not encouraging. But I'm very far from abandoning ship at least. I hope that this hasn't made you completely reconsider writing on the platform.
I think you're right that it's most likely just a matter of algorithms. I don't envy Medium in trying to sort a problem very few people can even understand. It amazes me that social media apps can function as well as they can at all. I doubt there's anything nefarious happening behind the scenes, and I still really do believe that Medium is a platform that advocates for its writers in ways that go beyond basically all of its competitors.
But yes, this is a pretty damn agonizing. Certainly the worst issue I've dealt with on the app since joining. Thanks for commenting and so sorry you're all dealing with this so soon after joining!!