If you aren’t on the same server, encryption doesn’t always work very well, and you semi-frequently end up with conversations where you can’t read each other’s messages. Id you try get signed out of your app on a given device, you’ll likely lose past conversations. Etc. It’s just… obnoxious.
Yup slim is what I’ve been using for ages. I’m disappointed that recently I can no longer get messages in it, but I accept that. Just have to open a browser and login there. Sigh