2) could be partially solved by backing up all of your keys from all devices. After that, non-decryptable messages decreased about 95%. Ironically, backing up

2) could be partially solved by backing up all of your keys from all devices. After that, non-decryptable messages decreased about 95%. Ironically, backing up your keys is done by recovering your keys from a backup – Settings → Cryptography Keys Management → Encrypted Messages Recovery → Restore from backup. (Web version: Settings → Security and Privacy → Key Backup → Restore from Backup) You can verify that you set it up properly by checking if the backups are signed by all your currently used devices (and possibly old ones, too). 3) can be mitigated by using workers. You'll need a beefy server, but message transfer and synchronisation will be super fast. The other things you mentioned are works in progress and I think the progress is outlined pretty transparently on Github, even if some people disagree with how the Matrix team is handling things.