"Blocked a frame with origin from accessing a cross-origin frame" when connecting via Nginx proxy

I’m trying to connect to Hass (v 0.71.0) through a Nginx proxy. Everything works fine until I click on the “Hass.io” menu to get to the add-ons. After that I get a flashing message “Service system_log/write called.” in the bottom left and in the logs I get a continuous stream of

2018-06-09 13:35:19 ERROR (MainThread) [frontend.js.latest.201806080b0] https://[url]/frontend_latest/5f865e9ebd4764019c14.chunk.js:14:449 Uncaught SecurityError: Blocked a frame with origin “https://[url]” from accessing a cross-origin frame.

After clicking that link you are unable to access anything else via the web ui until you refresh/reload the page.

This happens in incognito mode as well too.

Everything works fine when accessing the interface directly.

I’m also trying to access the same version, but on the local network - this error is coming up in the logs repeatedly. It doesn’t seem to be preventing access, just wondering what’s wrong…

I’ve restarted the system, and the error has stopped - for the moment