Errors occur when initializing and destroying the AR in quick succession.

[helloworld12321]

Sometimes we just get errors in the console:

but sometimes, if you initialize, destroy, and initialize the AR quickly, the <video> element doesn't appear in the DOM.

[helloworld12321]

I'm marking Marking as low-severity, since

1. you can recover from the white screen by pausing and unpausing, and
2. the actions that lead to this bug (pausing and unpausing frequently) are not very common.