[Fleet] After migrating Agents, agents are duplicated

[gergoabraham]

Kibana version: v8.12.2 Elasticsearch version: v8.12.2 Server OS version: just used https://console.qa.cld.elstc.co/

Describe the bug: After following the steps of Migrate Fleet-managed Elastic Agents from one cluster to another, I ended up with duplicated Fleet Agents on the new cluster: an offline, 'migrated' one and a newly enrolled one from every one of them.

The offline Agents have the same id in the new cluster, as in the original cluster. However, when enrolling the same agents, they will receive a new id.

Consequences

The users won't be able to see history/logs for a given Agent, because every agent has a new id.

For example, Response actions history: the user cannot see the full history of an Endpoint, as it will be separated for the 'old' and the 'new' Endpoint.

Old, 'migrated' agent:

Newly enrolled agent after performing processes response action:

The whole history:

which goes crazy when user tries to filter by host:

Steps to reproduce: Just follow the docs.

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[jlind23]

@gergoabraham thanks for reporting this but we know this is a limitation we have today. @nimarezainia is this something we should state in the docs?