Problem solved in private conversation. Initially I changed the hard pointers to soft pointers to be able to reference scene actors. However, we ran into what seems to be a bug, if someone can confirm a bug / share a solution?:
[5.1 / 5.1.1] Level Streaming >> -? Duplicated Actors ?-. - #6 by Roy_Wierer.Seda145
The direct issue of this post was solved by retrieving cameras by tag during runtime.