When seamlessly traveling, FNetworkObjectList will have its data cleared. However, because FNetworkObjectList::Reset is called before FNetworkObjectList::ResetDormancyState, AllNetworkObjects will be empty when resetting the dormancy state. This means that for dormant actors persisted through the travel, the DormantConnections on their FNetworkObjectInfo is not actually cleared in ResetDormancyState, but NumDormantObjectsPerConnection is still cleared as expected.
After travelling, FNetworkObjectList::MarkActiveInternal will hit a check if the actor is flushed/woken up, as "NetworkObjectInfo->DormantConnections.Remove(Connection) > 0" will return true while the NumDormantObjectsPerConnection is 0.
Dynamically spawn a dormant, replicated actor.
Seamlessly travel, ensuring that this actor is persisted through the entire travel on both the client and server.
Observer the check(NumDormantObjectsPerConnectionRef > 0) hit in FNetworkObjectList::MarkActiveInternal.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-200510 in the post.