User verification does not work on Conduit

### Steps to reproduce

1. register two users on a conduit homeserver
2. start emoji verification between element web and element ios
3. after the verification is done, the shield is still grey

When trying again between element web and another element web, user verification works, so this is a problem with ios.
Conduit sometimes sends to-device events multiple times or maybe in a wrong order, maybe that's an issue?

Start by reproducing the reported flow with two users on a Conduit homeserver: verify between Element Web and Element iOS, then compare it with Element Web to Element Web. Inspect the iOS handling of the to-device events involved in emoji verification, including duplicate or out-of-order delivery. Done means the verification shield is no longer grey after successful verification against Conduit.

Written by the indexing model from the issue text.