When creating a new instance of HA, due to issues or some other reason, the Aqara FP2 won’t be discoverable in the new instance unless you first remove it from the old HA instance. There is no other way to accomplish this. If you wait too long once you remove it from your old HA instance, you just need to unplug it and plug it back in and it will show in the HA instance.
The above is the solution if you’re unable to figure out why the Aqara FP2 isn’t being discovered by HA when creating a new instance after you’ve already added them to an old HA instance.