Two mutually verified users can not read each other's messages

[polynomialherder]

Describe the bug
Two users on my homeserver are using the latest iOS Element client (1.0.16) and have verified each other's devices. Each of these two users has one and only one device. Both users have shown me screenshots showing that the other's device is verified from their perspective. And yet frequently these users are not able to properly see each other's messages, with the

** Unable to decrypt: The sender's session has not sent us the keys for this message. **

placeholder text appearing in the place of the other's message. It appears that some messages become visible after a while (hours) and sometimes messages are visible immediately, but usually they cannot read each other's messages.

To Reproduce
As mentioned above, both clients are using the latest iOS Element client available in the Apple App Store (1.0.16) at the time of this writing. Both users have verified each other's devices. We are running Synapse 1.21.2

Expected behavior
I expect that two users sending messages from mutually verified devices should be able to see each other's messages at all times without ever seeing the ** Unable to decrypt placeholder text.

Aditional context
Other users on this homeserver are using the Linux desktop client or Android mobile clients (various versions, downloaded from f-droid). These users are able to read the messages of both users without problems.

The server is behind Cloudflare, with custom rules so that nothing is cached for the subdomain the matrix server lives on.

[inaiontcheva]

Please fix this, team. It's the only issue with the app. But it's been happening on and off for over an year and is so tiering wondering what the other person wrote...

[jakemoroni]

I'm having this same issue. It seems like the keys are randomly lost sometimes. Everything will be working fine, then poof, none of the messages are readable to one of the people in a 1-to-1 chat. Even newly sent messages are still unable to be decrypted.

In my opinion, this should be the highest priority bug for this app since it breaks the app's core functionality.

[inaiontcheva]

Agreed. Once it gets fixed, they should make an official announcement.

[yoman88111]

We experience the same issue.
Please, fix it, because our users doesn't receive critical info and the say it's very annoying..

[ara4n]

If you haven't submitted bug reports for the sender & receiving side of the broken conversations there is nothing we can do to hunt the bugs you're reporting. ANY problem with encryption results in "Unable to decrypt" errors. It could relate to your server, federation, a recent DoS we've seen on the network, client bugs, etc.

[jakemoroni]

I’ve opened a new issue for this (#3773
) since in my case, the users aren’t verified.

I’m waiting for it to happen again so I can submit the bug reports from the phones.

What I can say is that in my case, both clients were on a private homeserver. No federation.

[ara4n]

thanks. good news that they were both on the same server; should make it much easier to debug if/when it next happens.

[polynomialherder]

Thanks for the reply @ara4n

One of the impacted users is saying that the rage shake functionality isn't working for them, and they've confirmed that the setting is toggled in Settings -> Advanced. Adjusting the detection threshold doesn't seem to help matters. Is there a different way to submit a bug report?

The other user will try to submit a bug report soon -- I'll update when that happens

[polynomialherder]

The other user was able to submit a bug report!

More details

• Both users are on the same homeserver
• The homeserver is not federated since this is a private, personal group
• The synapse instance is running on a fairly beefy Ubuntu 18.04 DigitalOcean droplet running Apache behind Cloudflare (I've been careful to ensure that we aren't caching any of the Matrix endpoints)

[aaaaargZombies]

similar issues on group chats, will try to submit a log when it happens again

[jakemoroni]

@ara4n Just an update: I was finally able to capture this issue again and have my users submit rageshake bug reports, referencing issue #3773 in the description. I think it’s basically the same bug as this.

[ara4n]

There's a concrete chance this was fixed by #3817. @manuroe can you confirm?

[polynomialherder]

Excited to learn from @manuroe if this is indeed the case

@ara4n, if #3817 does fix this, will that reflect in the latest version on the app store?

[sjamaan]

No clue if this is exactly the same issue, but I had this today: I sent a picture from the desktop version of element-web to an iOS Element and it showed the dreaded ** Unable to decrypt: The sender's session has not sent us the keys for this message. **. There's a link saying "re-request encryption keys from your other sessions", however that shows a popup "request sent" and then nothing happens.

After sending a test message and then the same picture again from element-web it shows up on iOS, but the original message still shows the error message.

Perhaps it's notable that I happened to have updated the matrix-synapse server today (but it wasn't a race condition - I updated it earlier, before sending the message in question).