Hello Stephen,
By any chance, have you previously flashed any of the BLE example projects into your device? Some of the wireless examples put the device into low power mode, in which the debug modules are kept static or powered off depending on the low power level.
When using low-power features the board may not be found on discovery as debug modules can be affected.
When trying to flash/debug your application, please try to wake up the device by pressing repeatedly SW3/LLWU or Reset button (board) immediately after selecting "Debug" and while target discovery is trying to connect to the device.
If you are using a BLE example project, depending on the base project, inside app_preinclude.h you may find some macros related to low-power such as cPWR_UsePowerDownMode and cPWR_FullPowerDownMode; please disable (set to 0) these macros. After this, please try flashing/debugging the demo under this configuration.
Also, the Resurrect Kinetis device feature, part of the GUI Flash Tool, may be helpful.
Regards,
Eduardo.
