Keychat’s receiving address is updated using the Signal double ratchet, and so far rotating the receiving address has had almost no impact on the stability of message reception.

You've established yourself as the secure chat. No refute there. But you're not usable. -Notifications are shit. -No cross device support. -A sea of technical settings. -Backups are a disaster. -Delivery is iffy. Put the SIMPLE back in SimpleX, and make it as easy to use as Session. Pre-set all settings, clean the UX, make notifs work, add multi-device support, make backups easy and use a seed phrase to unlock them. Then you will be my go to. Till then, it's Session for me.

So the thing is that while Double Ratchet is a good encryption algorithm, MLS is a flawed implementation of it?

Honestly they should make it where if only one device can carry the chat database, then a desktop or server should be the primary device and then a phone or other devices can link to it. Their current solution of linking a mobile to a desktop doesn't really work (at least on iOS) because mobile devices have issues running background processes. I've never tried Session, and I don't know many people who use SimpleX. I do like SimpleX's idea of no accounts though (Session has accounts).

MLS uses ratcheting trees, it's different from Double Ratchet.