oops - the NRF52 build rules are suppose to inherit from arduino_base.

platformio.ini

@@ -172,7 +172,7 @@ build_flags =
   -Isdk-nrfxlib/crypto/nrf_oberon/include -Lsdk-nrfxlib/crypto/nrf_oberon/lib/cortex-m4/hard-float/ -lliboberon_3.0.3 
 ;-DCFG_DEBUG=3
 src_filter = 
-  ${env.src_filter} -<esp32/> -<nimble/> -<meshwifi/>
+  ${arduino_base.src_filter} -<esp32/> -<nimble/> -<meshwifi/>
 lib_ignore =
   BluetoothOTA
 monitor_port = /dev/ttyACM1