Even though the current code seems to be working fine, call KeyMatrix_Init() before InitKeyScanner() just to be sure.

left/src/init_peripherals.c

@@ -10,7 +10,6 @@
 #include "slave_protocol_handler.h"
 #include "i2c_watchdog.h"
 #include "debug_over_spi.h"
-#include "key_scanner.h"
 
 i2c_slave_config_t slaveConfig;
 i2c_slave_handle_t slaveHandle;
@@ -83,7 +82,6 @@ void InitLedDriver(void)
 void InitPeripherals(void)
 {
     InitInterruptPriorities();
-    InitKeyScanner();
     InitLedDriver();
     InitTestLed();
     LedPwm_Init();

left/src/main.c

@@ -4,6 +4,7 @@
 #include "bootloader.h"
 #include <stdio.h>
 #include "config.h"
+#include "key_scanner.h"
 
 DEFINE_BOOTLOADER_CONFIG_AREA(I2C_ADDRESS_LEFT_KEYBOARD_HALF_BOOTLOADER)
 
@@ -41,9 +42,9 @@ int main(void)
     InitClock();
     InitPeripherals();
     KeyMatrix_Init(&keyMatrix);
+    InitKeyScanner();
 
     while (1) {
-//        KeyMatrix_Scan(&keyMatrix);
         __WFI();
     }
 }