Not really, but ACL usually stands for access control list so it’s telling you that the connection Mastodon is trying isn’t authenticated. Are you using the same tokens for AWS? That could be a difference.
See if you can find a log on your server or if there is one on the S3 side where you can find more details.
Becuase you replied to it.
You only see the repos es that propagate to your instance. If you click on the 3 dots in webgui you can go to the original page. This will load straight from the senders instance and you will see their reality. From there you can get a link to a reply you wish to reply to and load that in your webgui. When you answer, your instance will make the connection and you will see responses from there in the future.
As the above suggests, you only see the instances your instance knows about. So following a hashtag is good but can also be limiting. But as soon as your instance learns of another instance it will be shown. So, from this, takeaway that it’s not an absolute nor consistent science.
I don’t really know, sorry. But I recommend https://fedi.tips for most things.
Side: yes. Very few uses the hashtags. But it doesn’t hurt if we try to improve.
Then join a more general server. There are literally tons of small general servers. Join one where they’re friendly. If you want to look “under the hood” before joining there are apps like ice cubes that lets you look at the local feed of each server. That way you can see who’s posting.