Thanks for your answer. In the mean time I solved the problem. The problem was solved by changing the MAC address of the different RPi 3B+ into the one of the RPi 3B+ on which the program worked. I used this post for this: https://scribles.net/changing-a-bluetooth-device-address-on-raspberry-pi/ App...

I wrote a C program to read weights via BLE from an electronic scale. It worked fine. Than I put the SD card in another RPi3B+ and it did not function correctly. It connected to the scale, but gives an error message when calling gattlib_connect. Note: the SD card was the same in both RPis. Any idea ...