Anonymous Group Chats
Group chats cannot be named, they are only listed by the members in the group chat listed alphabetically and comma separated. This makes differentiating group chats that share members from each other very difficult.

I assume this is to funnel users into using channels, but there are many short term conversations that don't necessarily fit into channels well, I feel that group chats are inevitable. If they wanted to funnel people I would go one step further and not allow group chats at all.
If I don't have the group chat members memorised for the conversation I am looking for, I need to click around through all of them till I find it.
This is compounded by another (great) feature: when a new person is added to a group chat, you can granularly select what part of the message history they are able to view.

Some of these options result in "message transfers", where instead of adding the new person to the group, it creates a fork of the group chat with all the original members plus the new ones, containing only the messages that the new person is allowed to see. The messages from the original group chat disappear. If I was not the person who created the forked group chat, its easy to lose track of what message is where.
This is compounded further by the next problem:
Direct Messaging Order
Slack shows direct messages ordered by:
- Unread messages
- Alphabetical
This is unhinged and unlike every single other messaging app ever made. It means that clicking a conversation immediately moves the conversation as it is no longer "unread" and cannot be at the top anymore.
To my brain this feels very unintuitive, and it makes it difficult to find recent messages that I've already ordered. This is doubly bad for group chats, triply bad for forked group chats.
Slack has a seperate DM screen that functions like a normal messaging app, the alphabetical order is only on the homescreen. I cannot justify this difference.