NodeMCU sensor flashed with ESPHome automatically restarts every 5 minutes

Home Assistant: 2020.12.7
ESPHome: v.1.15.3
Sensor: NodeMCU (with MQTT)

I have several NodeMCU sensors flashed with ESPHome using simple output-/switch configuration.
Over night my home assistant and MQTT servers are not available.

During that time my ESPHome based sensors do reboot every 5 minutes.
If I understand the documentation correctly then this should only happen if you use the keyword: “api” in *.yml configuration and I don’t use this. (see example configuration below)

Any ideas why my sensors reboots every 5 minutes?

Base configuration:

  name: ff_kitchen_relay_8ch_01
  platform: ESP8266
  board: d1_mini

  ssid: !secret wifi_ssid
  password: !secret wifi_password

# Enable logging
  level: INFO

  password: !secret ota_password
  broker: !secret mqtt_broker_ip
  username: !secret mqtt_username
  password: !secret mqtt_password

output and switches

What does your log say?