iOS back button text disappears
In a MvvmCross (latest stable) project with iOS the back button *sometimes* behaves likes this. When clicking it, the title text disappears and I have to click on the arrow on the left to go back:

![nav1](https://user-images.githubusercontent.com/1481801/116247371-12949a00-a76b-11eb-9909-1f0095f52498.gif)

I have also observed that holding down on the button (without releasing the mouse/finger) consistently makes the text dissappear:

![nav2](https://user-images.githubusercontent.com/1481801/116247388-16282100-a76b-11eb-86eb-06e997ccbe63.gif)

I'm not sure whether this is a MvvmCross problem or an iOS issue. Has anyone experienced someting similar?

This is a `MvxNavigationController` inside a `MvxTabController`.
