It’s a pain to switch between accounts. It eats up a ton of CPU if I use it through my browser (unless I use it in Firefox). If I use it in Firefox I can’t get video/voice calls or join up on meetings.

On a mobile device (iOS): It randomly logs me out (more like it will timeout if I haven’t opened the app recently). Notifications aren’t reliable. If I join a meeting with some other group as a “guest”, I can go back to view my active chat, but then I can only hear audio from the meeting and can’t get back to see what’s happening in the meeting unless I leave the room and come back.

There’s more, but this is just off the top of my head.