You might be right. If you check (on client) using “has Authority” for non-replicated Actors placed in a level, the result is “Is Remote”. If the client spawns a non-replicated Actor itself, the result of the Authority check is “Has Authority”. The client seems to believe it has no Authority over ordinary non-replicated Actors placed in the level (only the Actors it spawns itself).
Sadly, setting the owner to the local player-controller seems to have no effect. I’m not sure about trying to have the client change the RemoteRole. I’m currently in a Blueprints project, and there seems to be no way to set those values directly.
Ironically, the client can do everything else to placed Actors (set invisible, disable collision, disable Actor Tick, scale down to zero, move 100 miles away) but it can’t actually delete them. For now, making these Actors invisible and non-interactive seems to be the only workaround.