Thanks a lot for all your valuable advice. The UK 4K disc is brand new and it should not be damaged. I have local 4K disc (Aquaman)and it works well in my player.
Agree with cHing comments. All 4K discs are region free.
1 in a million chance (?), once I bought 4K Batman trilogy from Tak Fat basement, one of the three disc is slight defective.
Too rare, but it happened to me.
One more test, update player firmware. Only sometimes this is the cause.