`/keys/query` returning outdated device list for remote user

Opening this as a placeholder, rather than because I have something concrete to investigate right now.

We have rageshakes that show that, despite federation apparently working fine, `/keys/query` is not returning a device that was created (on a remote server) some time ago.

This obviously causes all sorts of problems, including UTD events and [failures to verify](https://github.com/element-hq/element-web/issues/29988).