why is the HRM-Dual not displaying correctly? already changed batttery, even using a new HR-Dual device, and reseted the Edge 530, but heart rate is not capture and display correctly

What do you mean - does it measure your heart rate wrong or does it not display your heart rate on 530 

During the weekend, I went on my regular bike rides and noticed that my average heart rate was around 100, whereas it used to be between 135 and 140. However, I suspect there may be an issue with my HRM-Dual device, as it intermittently loses connection and needs to be pulled to reconnect, only to lose connection again after a few minutes.

on my last ride, the average was 70, with max of 72, not real at all

How do you know it’s not real. Have you got a second device measuring your heart rate at the same time or are you assuming your heart rate is the same as it was in the past.