UIBarButtonItem-The background color of UIBarButtonItem is missing?

UIButton *backBtn = [UIButton buttonWithType:UIButtonTypeCustom];
backBtn.frame = CGRectMake(0, 0, 44, 44);
[backBtn setImage:[UIImage imageNamed:@"back"] forState:UIControlStateNormal];
[backBtn addTarget:self action:@selector(gotoBack) forControlEvents:UIControlEventTouchUpInside];

UIBarButtonItem *backItem = [[UIBarButtonItem alloc] initWithCustomView:backBtn];
//    backItem.hidesSharedBackground = YES;
//    backItem.tintColor = [UIColor redColor];
self.navigationItem.leftBarButtonItem = backItem;

I am using Xcode 26, which is compatible with iOS 26.

After I set up the back button of the navigation bar, why are the background colors of the back buttons on some pages gray? When I pushed the new page, after popping back to the current page, the buttons with the gray background turned back to the white background.

This issue will also affect the rightBarButtonItem.

UIBarButtonItem-The background color of UIBarButtonItem is missing?
 
 
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