DC 2nd device didn’t receive all messages after 1st device got multiple relays

[ghoffart]

• Operating System (Linux/Mac/Windows/iOS/Android): macOS (2nd device), iOS (1st device)
• Delta Chat Version: 2.49
• Expected behavior: all messages are delivered, or an error message is shown
• Actual behavior: Some messages in groups weren’t delivered.
• Steps to reproduce the problem: I added multiple relays (4) on my iOS device. After a few weeks of using it that way, I switched on a rarely used macOS computer, and updated DC immediately to 2.49. This 2nd DC didn’t show the multiple relays, but just 1. And in several groups (e.g. CCCFr public chat, ~104 users) I noticed that some messages didn’t get shown. This situation on the 2nd device didn’t resolve “magically” after a few days. I asked Holger about it and he hinted me into temporarily changing the default relay on the 1st device, and changing back. This lead to a) the multiple relays now shown on the 2nd device, and b) many missing messages were now delivered. He said I should file a bug. Here we are. :)
• Screenshots: n.a.
• Logs: n.a.

[WofWca]

Hey, thanks for the report!
Do you know which version you had on that rarely used machine before you updated?

This might have to do with this warning:

Anyways, looks like a Core issue. Whoever has access, please transfer.

[ghoffart]

2.48 on the 2nd device beforehand.

And the issue occured after updating and using the 2nd device to 2.49.

[hpk42]

if all relays were chatmail relays, they will have deleted after some weeks any multi-device-sync messages that the online device (which added the relays) sent to the long-offline device. We could re-send the relay-sync every N days, but the long-offline device would still miss messages which were also deleted.

Btw, if a long-offline device receives a multi-device-sync message with new relays, it will only look at the new relay's IMAP message list from now on, and not read the history, right? This design has more to do with how shared email address were once handled than with today's chatmail relays. It's probably a separate issue, though.

[ghoffart]

The missing messages on the 2nd device were from the same day, I basically looked at messages coming in on the 1st device, but not the 2nd, in near-real-time.

This was not an issue of weeks-old messages.

[hpk42]

were both devices sharing one relay at all times? Was that relay used for sending on the 1st device or some other relay? I am asking because if your chat partners have a pre-2.48 version they would only send back to the address where they got a message from you and that would go to a relay that the second device does not know before it receives a Multi-Device-Sync

[ghoffart]

Yes, all devices shared initially the same relay (mehl.cloud). I then added more on the 1st device (iPhone). Then, many many many weeks later, switched on 2nd device, updated DeltaChat to 2.49 on the 2nd, and kept using it.

I only found out that the 2nd device did not have the other relays added, too, by some magic, after I noticed that I am lacking many messages in a shared group, after a few weeks.

[link2xt]

Regarding missed messages, there is a related issue #7843 about not downloading messages from the added relay after relay synchronization.