Progress since the last snapshot is lost on a crash (at most one Snapshot Interval). A graceful leave sends a
final snapshot.
Not saved: in-flight RPCs, physics velocity, timers and animation state, unless you save them in
On Host Migration Save.
Actors without a Host Migration Id are not migrated. References to them only survive for placed actors.
Deltas work per record: a record that changes at all is resent whole. Large records that change often cost their
full size each interval.
A kept pawn (KeepInWorld) is a new actor with the old pawn's id and state. References to the old pawn object
from objects that are not migrated go stale.
References to PlayerStates of players who have not reconnected yet come back as null. Store the unique net id if
you need it later.
Soft object pointers (TSoftObjectPtr) to runtime-spawned actors do not survive. Use hard or weak pointers.
Rejoin and split-brain handling need an adapter with presence and announcements (Steam). With Null, two hosts
can still happen on LAN.
On Steam after a crash, clients keep trying to rejoin until Steam removes the crashed host from the lobby, which
delays the migration.