Instead of scanning the keyboard matrix from the main loop and utilizing busy loops, try to use a PIT interrupt handler to do the same thing, scanning one row per interrupt call without busy loops.

For some reason, this makes the movement of the mouse pointer very slow and makes it jump from time to time, so I ended up adding INTERRUPT_KEY_SCANNER and disabling the timer interrupt.
Also double bufferred the mouse report just like the others. Unfortunately this does not affect this issue.

right/src/main.h

@@ -7,14 +7,8 @@
     #include "slot.h"
     #include "module.h"
 
-// Macros:
-
-    #define KEYBOARD_MATRIX_COLS_NUM 7
-    #define KEYBOARD_MATRIX_ROWS_NUM 5
-
 // Variables:
 
-    extern key_matrix_t KeyMatrix;
     extern uint8_t PreviousKeyStates[SLOT_COUNT][MAX_KEY_COUNT_PER_MODULE];
     extern uint8_t CurrentKeyStates[SLOT_COUNT][MAX_KEY_COUNT_PER_MODULE];
     extern void UpdateUsbReports(void);