The issue was spotted when the ticket BLE_AGAMA-2149 has been tested and closed with version 4.20.00.24. During the test I tried several times perform unsuccessful connection to the slave running simple_peripheral app. Each attempt the Terminal correctly show Num Cons: 0. When I did successful connection of the devices the Num Cons still showed zero.
After reset of both devices and successful connection the terminal shows correct Num Cons: 1.