Zanzito mqtt problems

If i subscribe to zanzito/# topics into a terminal i get all the infos correct, but in HA i get device_info and status topics regularly. but NOT GPS updates… Where is the fault?
My device_tracker config is:

- platform: mqtt_json
  devices:
    maurizio: zanzito/shared_locations/S8
    fha: zanzito/shared_locations/fha

I also tried zanzito/S8/location but with no success.
My code inside configuration.yaml is:

mqtt:
  broker: !secret mqtt_broker
  username: !secret mqtt_username
  password: !secret mqtt_password
#  discovery: true
#  discovery_prefix: homeassistant

And i had all working till last releases of HA.
Can anybody help me to trace where is the error?
Is something changed in HA regarding MQTT components?