i agree, its not a big issue if you did not get into same problem as i have. in game development most of the time one large planar reflection is enough. For interior photo-realistic scene the use of planar reflection can be different.
I can understand you are surprised hearing about droping the project only for reflections because you are in game development where FPS is more important than photo-realism but in archviz photo-realism is the final thing above FPS. and most important client doesn’t care about you are working with realtime render or offline render or your software have limitations when it comes to video content all they care about final video with photo-realistic result delivered on time. may be this reflection is small thing for you but when video is played on big screen in 4k resolution anyone and your client can notice that.
and yes i come from offline render background and i have known unreal engine for very long time and knew it is made for game development thats why i never got onto this but things changed when Epic started promoting unreal engine as archviz development too with their promotional photo-real videos. I believed epic and was really excited but after getting into this problem i came to conclusion for archviz project you cant rely on100% on unreal engine.
and its not only about refection there are other things also when it comes to working on big project it can eat your time just fixing the bug or coming up with creative solutions to fix that and make you miss the deadline and lose your client. it is good for hobbyist otherwise some big company with big programmers team who can quickly fix the bug or come up with creative solutions.