As I stated, I'm very happy with the 4K disc so why should I bother to watch the Blu-ray looking for issues. I can understand you as a reviewer doing so, but I'm a happy camper.All I can say is what I see.
On my Sony 4K player and LG 4K OLED, the 4K appeared notably darker than the BD.
Did you compare the two? Maybe you'll think the BD looks too bright and the 4K "just right".
I found the BD more satisfying, but YMMV.