UActorChannel::SetChannelActor contains old code to synchronize the channel sequence numbers for a connection if the channel index is reused. This seems unnecessary now that we intentionally update the pending sequence number probably when the previous channel is cleaned up, wait for channels to acknowledge reliable bunches when they are closed, and have an option for randomizing the initial value of the sequence number (current code checks for and resets the value to 0).
When the synchronization bunch is sent, it "steals" the bOpen bunch for the actor channel, effectively preventing future bunches from spawning the actor on the client side. This code should likely be removed entirely.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-76950 in the post.