Flood of failed to connect errors [Errno -3]

After moving my HassIO from a RPi to a NUC-like (Zotac ZBOX C329 nano), I restored my latest config and most things went fine. For installation, I followed the following guide:

Running HassIO, version 0.93.1.

Currently, my log file is getting flooded with “Failed to connect” error messages for various components. The ones I observed giving that error are:

  • deutschebahn
  • steam
  • darksky
  • mqtt

As an example, for the steam component it looks like:
> 2019-05-19 17:32:20 WARNING (SyncWorker_3) [homeassistant.components.steam_online.sensor] Server took too long to respond

2019-05-19 17:32:44 ERROR (MainThread) [homeassistant.core] Error doing job: Task exception was never retrieved
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/homeassistant/helpers/entity.py", line 225, in async_update_ha_state
    self._async_write_ha_state()
  File "/usr/local/lib/python3.7/site-packages/homeassistant/helpers/entity.py", line 255, in _async_write_ha_state
    attr.update(self.state_attributes or {})
  File "/usr/local/lib/python3.7/site-packages/homeassistant/components/weather/__init__.py", line 121, in state_attributes
    self.hass, self.temperature, self.temperature_unit,
  File "/usr/local/lib/python3.7/site-packages/homeassistant/components/darksky/weather.py", line 106, in temperature_unit
    return TEMP_FAHRENHEIT if 'us' in self._dark_sky.units \
TypeError: argument of type 'NoneType' is not iterable
2019-05-19 17:32:51 WARNING (SyncWorker_6) [homeassistant.components.steam_online.sensor] Server took too long to respond

For the mqtt component, I repeatedly get these messages:

2019-05-19 17:33:14 ERROR (MainThread) [homeassistant.components.mqtt] Failed to connect due to exception: [Errno -3] Try again

2019-05-19 17:33:14 WARNING (MainThread) [homeassistant.config_entries] Config entry for mqtt not ready yet. Retrying in 80 seconds.

I am somewhat lost on finding the error, so hoping any of you might be able to help me out.

Same error here on a new install

Config entry for mqtt not ready yet. Retrying in 80 seconds.
7:22 AM config_entries.py (WARNING) - message first occured at 7:04 AM and shows up 14 times
Failed to connect due to exception: [Errno 111] Connection refused
7:22 AM components/mqtt/init.py (ERROR) - message first occured at 7:03 AM and shows up 18 times