Adding a 1s delay before sending ifconfig makes this test works reliably because it gives the softdevice enough time to get in a ready state.
Nordic SoftDevice Test Application
The main purpose of this test application is to ensure the inclusion of the Nordic SoftDevice package in RIOTs build test.
In addition, this example includes a minimal GNRC configuration and the
corresponding shell commands, so it can be used for some simple tests of
network functionality. Please refer to pkg/nordic_softdevice_ble/README.md
and pkg/nordic_softdevice_ble/README-BLE-6LoWPAN.md for more information on
how to setup an IPv6 connection to your device.
For more features, you can use the SoftDevice with RIOTs gnrc_networking
example application. Simply build gnrc_networking for a SoftDevice-capable
device, e.g. USEPKG=nordic_softdevice_ble BOARD=nrf52dk make ....