I configured my LAN adapter correctly to work Out-of-Home but after some time (15 or more minutes) the units are indicated as offline and remote control is blocked.

Please ensure that the date and time of the Daikin Altherma user interface doesn’t differ more than 15 minutes with the date and time that the smartphone uses for Out-of-Home control. If it differs more than 15 minutes, the application will indicate the units as offline.