[REG 5.4.1 -> 5.5 beta] Some pages show up blank after flashing quickly

With the 5.5 beta, some pages quickly flash up and then are rendered completely blank, for example:

https://www.python.org/dev/peps/pep-3119/

I've had this happen on at least one other page, but I don't remember the URL.

When resizing the window to be smaller (so the mobile view is shown), it renders fine, as soon as the window gets bigger again it's blank again.