core: mobile_app generated webhook error

Home Assistant release with the issue:

0.103.0

Last working Home Assistant release (if known): 0.102.3

Operating environment (Hass.io/Docker/Windows/etc.):

arch | armv7l
-- | --
dev | false
docker | true
hassio | false
os_name | Linux
python_version | 3.7.5
timezone | America/Los_Angeles
version | 0.103.0
virtualenv | false

Integration:

https://www.home-assistant.io/integrations/mobile_app/

Description of problem: After updating to 0.103.0 I checked the logs and found that there was a webhook error that used the same ID as the one for my mobile_app device. This has showed up once in the logs per restart and happens about 18 hours after restart (I has happened twice).

Problem-relevant configuration.yaml entries and (fill out even if it seems unimportant):

mobile_app:

Traceback (if applicable):

2019-12-12 19:47:25 ERROR (MainThread) [homeassistant.components.webhook] Error processing webhook ****webhook*that*matches*.storage/mobile_app*device*6c9
Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/components/webhook/__init__.py", line 77, in async_handle_webhook
    response = await webhook["handler"](hass, webhook_id, request)
  File "/usr/src/homeassistant/homeassistant/components/mobile_app/webhook.py", line 275, in handle_webhook
    await hass.data[DOMAIN][DATA_STORE].async_save(safe)
  File "/usr/src/homeassistant/homeassistant/helpers/storage.py", line 137, in async_save
    await self._async_handle_write_data()
  File "/usr/src/homeassistant/homeassistant/helpers/storage.py", line 198, in _async_handle_write_data
    self._write_data, self.path, data
concurrent.futures._base.CancelledError

Additional information: