This is happening because ecobee stopped reporting weather data last night. Beestat requires a certain minimum set of data points in order for a set of data to be considered accurate. If any one of those points are missing it throws away the data as inaccurate. There are some technical reasons for this which I can go into if you are interested.
But basically outdoor temperature is one of those required data points. Since ecobee stopped providing it, beestat is assuming recent data is bad and is not syncing it. Good news is that as soon as ecobee fixes the issue beestat will start working automatically. If ecobee also happens to restore the missing data then beestat will capture that as well.