When a zone goes dead and you look at the trend data for the zone, it is a common misconception that you are getting data, when in fact the zone is dead. The way 75F interpolates data is that if we have received a value during the selected date range is to report the last known value until the current time.
The reason we do this is that it isn't uncommon to lose communication for short periods. So rather than showing immediate sporadic drops to 0 or no value, we fill the gaps.
So lets look at this example. I am looking at Dec21-Dec22. I lost communication to the zone at 12:24pm on Dec 22nd. But the data kept reporting the last known value. So the most important thing to look for is if the equipment is connected.
Now if you look at the same zone for the day of Dec23. You will see the no data is available. This is because there is nothing to fill in for the given date range.