Alarm Control Panel Suddenly Failing to Load

I restarted my HASS install (0.85.0) and when it started back up I’m getting the following error:

Fri Feb 01 2019 15:29:10 GMT+0000 (Greenwich Mean Time)

Error doing job: Task exception was never retrieved
Traceback (most recent call last):
  File "/usr/src/app/homeassistant/helpers/entity_platform.py", line 350, in _async_add_entity
    await entity.async_added_to_hass()
  File "/usr/src/app/homeassistant/components/alarm_control_panel/manual.py", line 318, in async_added_to_hass
    state.attributes['pre_pending_state']:
KeyError: 'pre_pending_state'

I’ve not changed anything so it’s pretty weird. I’ve tried upgrading to 0.86.4, deleting my home assistant DB, but it just doesn’t work. I’m basically alarmless!

My config is (which hasn’t changed)

alarm_control_panel:
  platform: manual
  code: !secret alarm_panel_code
  name: "HA Alarm"
  disarm_after_trigger: true
  pending_time: 45
  trigger_time: 120

Weirdly if I create a new alarm panel with a different name, that one appears fine. I guess I can rename all my automations to use the new entity, but it’s pretty odd…