UITabBar items jumping on back navigation on iOS 12.1

Apple has now fixed that in iOS 12.1.1

I guess it's Apple's bug But you can try this as a hot fix: just create a class for your tabBar with following code:

import UIKit

class FixedTabBar: UITabBar {

    var itemFrames = [CGRect]()
    var tabBarItems = [UIView]()


    override func layoutSubviews() {
        super.layoutSubviews()

        if itemFrames.isEmpty, let UITabBarButtonClass = NSClassFromString("UITabBarButton") as? NSObject.Type {
            tabBarItems = subviews.filter({$0.isKind(of: UITabBarButtonClass)})
            tabBarItems.forEach({itemFrames.append($0.frame)})
        }

        if !itemFrames.isEmpty, !tabBarItems.isEmpty, itemFrames.count == items?.count {
            tabBarItems.enumerated().forEach({$0.element.frame = itemFrames[$0.offset]})
        }
    }
}

In your UITabBarController, set isTranslucent = false