This has been my experience with Matrix, and the message decryption problems are a dealbreaker. I hope the person who replied to you saying those have very recently been fixed is correct, but the fact that such a fundamental feature was broken for so long leaves me with little confidence in Matrix. I had this problem years ago on a Matrix community, then again maybe a year ago on a different community, and even more recently on my self-hosted instance. Don’t understand how you can push a chat platform that effectively doesn’t deliver ~1/12 messages to random users and let that issue hang around for years.

XMPP looks really interesting as an alternative. Hope that development continued at a brisk pace.