This seems to be an issue with IonRouterOutlet.
I’m also getting double rendering on every component once it’s been mounted. As @GuillermoDotAt said, you can easily duplicate this by using the starter ionic react app. Using the side menu starter app, the component double renders each time you click a menu nav.
In my own app, every component will double render every time I change routes as long as they’ve been mounted. For example, once I’ve navigated to RouteA, RouteA is rendering twice every time I change routes.
<Switch>, the components are only rendered once as expected, but you lose access to navigation animations and the ionSplitPane, so I’d rather not do that!