Weak bluetooth link

Samsung S7, android 8.0, Bluetooth 4.2
Nuki smart lock pro 3.0, firmware 3.6.9

finding the smart Lock was difficult. It failed 2 time before success.
updating the firmware failed 2 times before success.
I had to put the smartphone close to the nuki smart lock (< 10 cm)

after that the status of the bluetooth connection permanently switch before yellow and green.

this is the first time I get many problems with bluetooth.