Bug: back/forward button leads to graphical artifact (missing context?) for Simple3DScene

[mkhorton]

Behavior: When navigating to a new page where a Simple3DScene is on both the previous and new page, sometimes the scene is replaced with a pink square (observed Safari 13.1.2). Clicking inside the scene restores the scene correctly. Suspect some issue with React lifecycle.

Haven't get got a small, re-producible example, so can hold-off fixing until easier to replicate.