Since a recent sw/fw update of the Edge 1030+, the temperature is at least 4 to 5 degrees Celsius too high.
The issue gets worse if it is sunny weather.
It seems that Garmin took an old branch of SW version where this bug was in but did not correct it. This issue is reported 2 years ago as well. Then it disappeared and now it is back so it seems a recurring bug/major issue.
Garmin fix this major issue for good as it makes quite some training data useless for comparison and the user cannot get any work around.