I've found that issue can be solved by opening the same chat on your multiple devices at the same time, and it will send the E2E keys across. I'm thinking this

I've found that issue can be solved by opening the same chat on your multiple devices at the same time, and it will send the E2E keys across. I'm thinking this may be a messaging issue rather than a technical bug in some cases - `Unable to decrypt: The sender's device has not sent us the keys for this message` isn't very helpful. I think while this isn't ideal, it's important to note (for those following along) that neither Signal, Telegram or WhatsApp support end-to-end encryption across desktop and mobile, history syncing to new devices, and a self hosted OSS server with multiple client apps.