[solved] MQTT sensor not updating

Edit: Solved! It was my fault. I was confused about the actual topic.

I have a MQTT sensor that isn’t updating sometimes for like half a day at a time. Then it starts working again for reasons I haven’t been able to identify. Restarting HA sometimes fixes it and sometimes not. I know the MQTT messages are coming in, and I can subscribe to the MQTT broker and see the sensor data posted. But home assistant’s MQTT sensor isn’t updating. It’s an intermittent problem.

What’s a good way to troubleshoot this?

sensor:
  - platform: dnsip
    name: homeIP
    scan_interval: 3600
  #MQTT Sensors---
  - platform: mqtt
    state_topic: "temp/ff"
    name: Kids Room Temp
    unit_of_measurement: 'f'
    icon: mdi:temperature-fahrenheit

More info:

I can see the core system log loading the MQTT component:

2020-05-29 09:17:21 INFO (SyncWorker_5) [homeassistant.loader] Loaded hassio from homeassistant.components.hassio
2020-05-29 09:17:21 INFO (SyncWorker_4) [homeassistant.loader] Loaded switch from homeassistant.components.switch
2020-05-29 09:17:21 INFO (SyncWorker_7) [homeassistant.loader] Loaded logger from homeassistant.components.logger
2020-05-29 09:17:21 INFO (SyncWorker_9) [homeassistant.loader] Loaded mqtt from homeassistant.components.mqtt
2020-05-29 09:17:21 INFO (SyncWorker_6) [homeassistant.loader] Loaded group from homeassistant.components.group
2020-05-29 09:17:21 INFO (SyncWorker_0) [homeassistant.loader] Loaded automation from homeassistant.components.automation
2020-05-29 09:17:21 INFO (SyncWorker_3) [homeassistant.loader] Loaded scene from homeassistant.components.scene

I don’t see any other mentions of MQTT in the core logs.