CCS/MSP430FR2355: MSP430FR2355 RTC Seems to crash registers after some time

#include <msp430.h>
#include <stdint.h>

//#pragma LOCATION(rtcState, 0x660); //Backup memory remains powered during LPM3.5
//volatile struct Time {
//    uint8_t  seconds;
//    uint8_t  minutes;
//    uint8_t  hours;
//} rtcState;
uint8_t seconds;
uint8_t minutes;
uint8_t hours;
int cnt;


int main(void)
{
    WDTCTL = WDTPW | WDTHOLD;               // Stop watchdog timer

    P2SEL1 |= BIT6 | BIT7;                  // P2.6~P2.7: crystal pins


    CSCTL4 = SELMS__DCOCLKDIV | SELA__XT1CLK;  // MCLK=SMCLK=DCO; ACLK=XT1

       // Port Configuration all un-used pins to output low
       P1OUT = 0x00; P2OUT = 0x00;
       P3OUT = 0x00; P4OUT = 0x00;
       P5OUT = 0x00; P6OUT = 0x00;
       P1DIR = 0xff; P2DIR = 0xff;
       P3DIR = 0xff; P4DIR = 0xff;
       P5DIR = 0xff; P6DIR = 0xff;

       // Disable the GPIO power-on default high-impedance mode
       // to activate previously configured port settings
       PM5CTL0 &= ~LOCKLPM5;

       do
       {
           CSCTL7 &= ~(XT1OFFG | DCOFFG);      // Clear XT1 and DCO fault flag
           SFRIFG1 &= ~OFIFG;
       }while (SFRIFG1 & OFIFG);               // Test oscillator fault flag


    // RTC count re-load compare value at 32.
    // 1024/32768 * 32 = 1 sec.
    RTCMOD = 32-1;
                                            // Initialize RTC
    // Source = 32kHz crystal, divided by 1024
    RTCCTL = RTCSS__XT1CLK | RTCSR | RTCPS__1024 | RTCIE;

    if (SYSRSTIV == SYSRSTIV_LPM5WU)        // When woken up from LPM3.5, reinit
        {
            // If MCU wakes up from LPM3.5, re-init and then return to LPM3.5 again.
        __no_operation();                       // For debug
        }
        else
        {
            // Device powered up from a cold start.
            __no_operation();                       // For debug
        }
    //This is for LPM3.5
    //PMMCTL0_H = PMMPW_H;                    // Open PMM Registers for write
    //PMMCTL0_L |= PMMREGOFF;                 // and set PMMREGOFF

    seconds=0;
    minutes=0;
    hours=0;
    cnt=0;

    __bis_SR_register(LPM3_bits | GIE);     // Enter LPM3, enable interrupt
    __no_operation();                       // For debug
}

// RTC interrupt service routine
#if defined(__TI_COMPILER_VERSION__) || defined(__IAR_SYSTEMS_ICC__)
#pragma vector=RTC_VECTOR
__interrupt void RTC_ISR(void)
#elif defined(__GNUC__)
void __attribute__ ((interrupt(RTC_VECTOR))) RTC_ISR (void)
#else
#error Compiler not supported!
#endif
{
    switch(__even_in_range(RTCIV,RTCIV_RTCIF))
    {
        case  RTCIV_NONE:   break;          // No interrupt
        case  RTCIV_RTCIF:                  // RTC Overflow

            if(cnt>1019) {
                __no_operation();                       // For debug
            }

            if(seconds > 60) {
                __no_operation();                       // For debug
            }
cnt++;
            seconds++;
            P1OUT ^= BIT0;
            if(seconds >= 60) {
                seconds = 0;
                P1OUT ^= BIT0;
                minutes++;
                if(minutes >= 60) {
                    P1OUT ^= BIT0;
                    minutes = 0;
                    hours++;
                    if(hours >= 24) {
                        hours = 0;
                        P1OUT ^= BIT0;
                    }
                }
            }


            break;
        default: break;
    }
    __bis_SR_register(LPM3_bits | GIE);     // Enter LPM3, enable interrupt
    __no_operation();                       // For debug
}