After hours of research I found that in LayoutAnchorSideControl, in the LayoutAnchorSideControl_Unloaded method, for some reason, it's removed the collectionChanged handler on the model's children
_model.Children.CollectionChanged -= OnModelChildrenCollectionChanged;
Removing this line from the code everything works fine.
It seems that is the root of a lot of other Issues opened around the load of a different theme.

It's easy to reproduce on the MVVMTestApp