Per mikeller's comment.

lib/main/STM32_USB_OTG_Driver/src/usb_core.c

@@ -392,12 +392,9 @@ USB_OTG_STS USB_OTG_CoreInit(USB_OTG_CORE_HANDLE *pdev)
     /* Deactivate the power down*/
     gccfg.d32 = 0;
     gccfg.b.pwdn = 1;
-#ifdef VBUS_SENSING_ENABLED
-    gccfg.b.vbussensingA = 1 ;
-    gccfg.b.vbussensingB = 1 ; 
-#else
+
+    // XXX Betaflight mod; disabled VBUS sensing features completely, including Sense A and B.
     gccfg.b.disablevbussensing = 1; 
-#endif    
 
     if(pdev->cfg.Sof_output)
     {

src/main/drivers/usb_io.c

@@ -59,7 +59,9 @@ bool usbCableIsInserted(void)
     bool result = false;
 
 #ifdef USE_USB_DETECT
-    result = IORead(usbDetectPin) != 0;
+    if (usbDetectPin) {
+        result = IORead(usbDetectPin) != 0;
+    }
 #endif
 
     return result;

src/main/target/KROOZX/target.h

@@ -95,8 +95,6 @@
 #define CURRENT_METER_OFFSET_DEFAULT   0
 
 #define USE_VCP
-#define USE_USB_DETECT
-//#define USB_DETECT_PIN          PA9
 
 #define USE_UART1
 #define UART1_RX_PIN            PA10