TCB timer on ATMEL ATMEGA4809 not as advertised

[alantrow]

I started with microchip's own "TB3214-Getting-Started-with-TCB-90003214A.pdf". in "Example 7-3. TCB Sleep Mode Operation Code Example" I followed their example as closely as I can possibly get in my custom board (one with an RGB LED). The board goes into low power - no CPU - but no LED blinking from the TCB timer interrupt. I have no idea where to turn next.

Here's my code - with changes from the example noted in comments:

#include <atmel_start.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/sleep.h>

#define TCB_CMP_EXAMPLE_VALUE (0x7FFF)

#define RGB_R_PORT VPORTE /* Change from example /
#define RGB_R_PIN PIN0_bm / Change from example */

#define RGB_G_PORT VPORTE /* Change from example /
#define RGB_G_PIN PIN1_bm / Change from example */

#define RGB_B_PORT VPORTE /* Change from example /
#define RGB_B_PIN PIN2_bm / Change from example */

void CLOCK_init (void);
void SLPCTRL_init (void);
void PORT_init (void);
void TCB0_init (void);

void CLOCK_init (void)
{
/* Enable writing to protected register /
CPU_CCP = CCP_IOREG_gc;
/ Disable CLK_PER Prescaler /
CLKCTRL.MCLKCTRLB = 0 << CLKCTRL_PEN_bp;
/ Enable writing to protected register /
CPU_CCP = CCP_IOREG_gc;
/ Select 32KHz Internal Ultra Low Power Oscillator (OSCULP32K) /
CLKCTRL.MCLKCTRLA = CLKCTRL_CLKSEL_OSCULP32K_gc;
/ Wait for system oscillator changing to finish */
while (CLKCTRL.MCLKSTATUS & CLKCTRL_SOSC_bm)
{
;
}
}

void SLPCTRL_init (void)
{
/* Enable sleep mode and select Standby mode */
SLPCTRL.CTRLA = SLPCTRL_SMODE_gm | SLPCTRL_SMODE_STDBY_gc;
}

void PORT_init (void)
{
RGB_R_PORT.DIR |= RGB_R_PIN; /* Change from example /
RGB_G_PORT.DIR |= RGB_G_PIN; / Change from example /
RGB_B_PORT.DIR |= RGB_B_PIN; / Change from example */
}

void setRed(bool state) /* Change from example */
{
if (state)
RGB_R_PORT.OUT |= RGB_R_PIN;
else
RGB_R_PORT.OUT &= ~RGB_R_PIN;
}

void setGreen(bool state) /* Change from example */
{
if (state)
RGB_G_PORT.OUT |= RGB_G_PIN;
else
RGB_G_PORT.OUT &= ~RGB_G_PIN;
}

void setBlue(bool state) /* Change from example */
{
if (state)
RGB_B_PORT.OUT |= RGB_B_PIN;
else
RGB_B_PORT.OUT &= ~RGB_B_PIN;
}

void TCB0_init (void)
{
/* Load the Compare or Capture register with the timeout value*/
TCB0.CCMP = TCB_CMP_EXAMPLE_VALUE;
/* Enable TCB and set CLK_PER divider to 1 (No Prescaling) /
TCB0.CTRLA = TCB_CLKSEL_CLKDIV1_gc | TCB_ENABLE_bm | TCB_RUNSTDBY_bm;
/ Enable Capture or Timeout interrupt */
TCB0.INTCTRL = TCB_CAPT_bm;
}

ISR(TCB0_INT_vect)
{
TCB0.INTFLAGS = TCB_CAPT_bm; /* Clear the interrupt flag /
// setRed(true);
PORTE.IN = RGB_R_PIN; / Toggle PBE GPIO / / Change from example */
}

int main(void)
{
CLOCK_init();
SLPCTRL_init();
PORT_init();
TCB0_init();
sei(); /* Enable Global Interrupts */

setRed(false);	    /* Change from example - change the LEDs to off */
setGreen(false);	/* Change from example */
setBlue(false);	    /* Change from example */

while (1)
{
	sleep_mode();
}

}

ANY CLUES?