In splitscreen, Player 0 view influences reflections for other player views. A user submitted the included test project showing the issue, and I have reproduced on 4.18.3 as well as 4.19.2 (see SplitReflect_1.gif).
I was also able to observe the issue with Planar reflections in ShooterGame sample project (see SplitReflect_2.gif).
Result: Player 0 shows correct reflections, Player 1 reflections appear to be influenced by Player 0 view; see attached GIFs
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-59149 in the post.