What could cause localStorage to be null? (Chrome / Android)

Question

I see in error tracking software that 0.25% of users have encountered this problem. The only template I can see is Android 6.0.1 / 5.1.1 and Chrome 54 or 55. What can cause localStorage to be null? This is a web application (not wrapped in WebView), and when you disable the ability to set user data, it actually throws an exception when trying to access it, rather than setting it to null.

Hooray!