0.81.0b0 History Tooltips Not Displaying

[mynameisdaniel32]

Home Assistant release with the issue:
0.81.0b0

Last working Home Assistant release (if known):
0.80.3

Browser and Operating System:
Firefox 62.0.3
Opera 56.0.3051.52 (latest)
Windows 10

Chrome doesn't seem to be affected.

Description of problem:
When hovering over the history graph on the more-info popup for an entity, either graph or timeline, instead of showing a tooltip with the value, an error is written (with the little box notifying 'Service system_log/write called'). I have tried clearing the browser caches without change.

This only occurs in the original frontend, my test lovelace page shows the tooltips fine in the same browsers.

In the logs, an entry like this is created:
2018-10-22 12:03:07 ERROR (MainThread) [frontend.js.latest.201810210] https://REDACTED/frontend_latest/app-3d20ffc0.js:4979:1961 Uncaught TypeError: Cannot read property 'language' of undefined

Javascript errors shown in the web inspector (if applicable):

TypeError: this.hass is undefined[Learn More]

Additional information: