crash when clearing uint8_t on pic18f67k22

Question

I'm adding a clock to my program, but for some reason I cannot lower the value of my "sec" variable.

I have a millisecond timer that raises a flag every ms. So, every 1000 ms I clear the ms variable; this happens without a problem.

Now every 10 (for debug purposes) seconds I want to clear the sec variable and everything stops.

I'm using a pic18f67k22.

I should just be able to assign 0 to it, and it is VERY frustrating. Every value below 10 crashes; values above 10 resume like nothing happened.

minimal reproducible example, I left out lcd code as it was just for me to see if it still happened with minimal code, left out delay because it's just a bunch of "nop"'s, fuses and pin.h do not appear relevant either, fuses might be but your pins would be different): main.c:

#include "fuses.h"

#include <stdbool.h>
#include <stdio.h>
#include <xc.h>

#include "clock.h"
#include "interrupt.h"
#include "LCDSerialTerminalMaster.h"

uint8_t prevSec = 0;

void main(void)
{
    // disable comparators
    CM1CONbits.CON = 0;
    CM2CONbits.CON = 0;
    CM3CONbits.CON = 0;
    // disable analog input
    ADCON0bits.ADON = false;
    ANCON0 = 0;
    ANCON1 = 0;
    ANCON2 = 0;
    
    INT_Init();
    CLK_Init();
    LCD_Init();

    
    while(1)
    {
        if(CLK_GetSec() != prevSec)
        {
            prevSec = CLK_GetSec();
            
            LCD_Write();
        }
    }
    
}

interrupt.c:

#include <stdbool.h>

#include "interrupt.h"

#include "clock.h"
#include "pin.h"
void INT_Init(void)
{
    // Enable Interrupt Priority Vectors
    IPEN = 1;

    // RCI - high priority
    UART1_RC_IP = 1;
    UART2_RC_IP = 1;
    
    UART1_TX_IP = 0;
    UART2_TX_IP = 0;

    MASTER_SYNC_IP = 1;
    
    INT_Toggle(true);
}

void INT_Toggle(bool toggle)
{
    INT_ToggleHigh(toggle);
    INT_ToggleLow(toggle);
}

void INT_ToggleHigh(bool toggle)
{
    INTCONbits.GIEH = toggle;
}

void INT_ToggleLow(bool toggle)
{
    INTCONbits.GIEL = toggle;
}

void __interrupt() INT_InterruptManagerHigh(void)
{
    
    if(PIR4bits.CCP4IF)
        CLK_ISR();
    
}

clock.c

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <xc.h>

static uint8_t hour = 0;
static uint8_t min = 0;
static uint8_t sec = 0;
static volatile uint16_t ms = 0;

void CLK_Init(void)
{
    T3CONbits.TMR3CS = 0b00; // Source = Fosc/4
    T3CONbits.SOSCEN = 0b1;  // SOSC disabled
    T3CONbits.T3CKPS = 0b00; // Prescaler 1:1

    CCP4CONbits.CCP4M = 0b1011; // Compare Mode: Special Event Trigger, reset TMR3 on CCP4 match
    CCPTMRS1bits.C4TSEL = 0b01; // TMR3/TMR4

    // set compare value to 5000
    CCPR4L = 136;
    CCPR4H = 19;

    // Disable TMR3 interrupt.
    PIE2bits.TMR3IE = 0;

    // clear CCP4 interrupt.
    PIR4bits.CCP4IF = 0;

    // enable CCP4 interrupt.
    PIE4bits.CCP4IE = 1;
    IPR4bits.CCP4IP = 1;

    // Start the Timer by writing to TMRxON bit.
    T3CONbits.TMR3ON = 1;
}

void CLK_GetTime(char *buffer)
{
    sprintf(buffer, "%02hhu:%02hhu:%02hhu", hour, min, sec);
}

uint8_t CLK_GetSec(void)
{
    return sec;
}

void CLK_ISR(void)
{   
    PIR4bits.CCP4IF = 0;
    ms++;
    if(ms == 1000)
    {
        ms = 0;
        sec++;
        if(sec == 10)
        {
            sec = 0;
            min++;
            if(min == 60)
            {
                min = 0;
                hour++;
                if(hour == 24)
                    hour = 0;
            }
        }
    }
}

the error happens in CLK_ISR, I can't assign a value lower than the value i'm comparing to, if I try sec-- the same thing happens.