Invalid config: default_config could not be set up

I recently upgraded Home Assistant to 2021.12 and now I cannot access it through the iOS app. I get a mostly blank screen with just this error message: An SSL error has occurred and a secure connection to the server cannot be made. NSURLErrorDomain -1200. I have a Home Assistant Cloud account with Nabu Casa and that’s how I normally am able to connect to my Home Assistant when traveling.

But I think the above symptom is due to the problem I’m about to describe below. I’m currently away from home, but I can connect through WireGuard (running as a Home Assistant add on) to the web interface on my home LAN. When I do that, there’s a notification in the web UI:

Invalid config
The following integrations and platforms could not be set up: default_config
Please check your config and logs

I did the configuration check on the Server Controls page and it says my configuration is valid. My configuration.yaml is included below.

There are some interesting messages in the logs

[homeassistant.components.websocket_api.http.connection] [548142523296] Received invalid command: mobile_app/push_notification_channel
2021-12-15 09:38:51 WARNING (MainThread) [homeassistant.setup] Setup of cloud is taking over 10 seconds.
2021-12-15 09:38:54 ERROR (MainThread) [homeassistant.components.websocket_api.http.connection] [548142523296] Received invalid command: mobile_app/push_notification_channel
2021-12-15 09:39:39 WARNING (MainThread) [homeassistant.bootstrap] Waiting on integrations to complete setup: cloud
2021-12-15 09:40:39 WARNING (MainThread) [homeassistant.bootstrap] Waiting on integrations to complete setup: cloud
2021-12-15 09:41:39 WARNING (MainThread) [homeassistant.bootstrap] Waiting on integrations to complete setup: cloud
2021-12-15 09:41:39 WARNING (MainThread) [homeassistant.bootstrap] Setup timed out for stage 1 - moving forward
2021-12-15 09:41:50 ERROR (MainThread) [homeassistant.components.websocket_api.http.connection] [548142523296] Received invalid command: mobile_app/push_notification_channel
2021-12-15 09:42:10 ERROR (MainThread) [homeassistant.components.updater] Timeout fetching Home Assistant update data
2021-12-15 09:42:40 WARNING (MainThread) [homeassistant.bootstrap] Waiting on integrations to complete setup: cloud
2021-12-15 09:43:40 WARNING (MainThread) [homeassistant.bootstrap] Waiting on integrations to complete setup: cloud
2021-12-15 09:43:41 ERROR (MainThread) [homeassistant.setup] Setup of cloud is taking longer than 300 seconds. Startup will proceed without waiting any longer
2021-12-15 09:43:41 ERROR (MainThread) [homeassistant.setup] Unable to set up dependencies of default_config. Setup failed for dependencies: cloud
2021-12-15 09:43:41 ERROR (MainThread) [homeassistant.setup] Setup failed for default_config: Could not set up all dependencies.

Here’s my configuration.yaml

# Configure a default setup of Home Assistant (frontend, api, etc)
default_config:

# Text to speech
tts:
  - platform: google_translate

# Light groups go in lights.yaml, not groups.yaml
# https://community.home-assistant.io/t/please-help-with-groups-yaml/290659/2
light: !include lights.yaml

group: !include groups.yaml
automation: !include automations.yaml
script: !include scripts.yaml
scene: !include scenes.yaml

# Email Notification
notify: !include notify-email.yaml

sensor: !include iotlink-sensors.yaml

# Shades
cover: !include covers.yaml

# Cameras
camera: !include cameras.yaml

… and now it’s fixed. I had tried rebooting my Raspberry Pi before and it didn’t help. I tried rebooting one more time after posting this and everything seems to be working again. I guess this was some kind of transient failure?