Hi,
Hope you are doing well.
As you might know, some of the wireless examples put the device into low power mode, in which the debug-related modules are kept static or powered off depending on the low power level and the board may not be found on discovery.
Could you please confirm if you have tried the following procedure? When trying to flash/debug your application, 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 gAppLowpowerEnabled_d; please disable (set to 0) this macro. 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.