Users whose servers were unreachable when you logged in will send you undecryptable messages

[matrixbot]

This issue has been migrated from #2165.

---

• Alice logs in on a new device
• Alice's server tries to tell everyone about her new device
• Bob's server is unreachable at that moment
• Later, Bob sends a message. He doesn't know about Alice's new device. Alice sees a UISI.

[richvdh]

This isn't really a synapse issue. It's a protocol issue really, but filing it under element-meta along with the other UTD issues: element-hq/element-meta#2314