NRF54L15 Timer running much slower than expected

Question

Running on Fanstel BM15M module (nrf54L15) SDK v3.1.1, I seeing a huge timing error when trying to implement a simple timer function. In the code below, I believe I have followed the examples to implement a timer (24) with a 1MHz frequency and a 100 count interval which should yield a 10kHz interrupt. But using the callback function to toggle a debug pin and monitoring that pin with an O'scope, I see a stable 128us interval instead of 100us - a 28% error. I am running off the internal oscillator. The internal crystal is 250ppm which should yield at most an error 2.5us 
 Please tell me what I am doing wrong. Side note when I try to use the external 32MHz crystal per the notes provided by Fanstel, I get stuck with an assertion error - "err = mpsl_init(&clock_cfg, CONFIG_MPSL_LOW_PRIO_IRQN, m_assert_handl" - but that is perhaps a discussion for another day. 
 prf.conf lines: 
 
 CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC =y 
 CONFIG_CLOCK_CONTROL_NRF_K32SRC_250PPM =y 
 
 Timer setup in main.c:

/****************** Main Loop timer setup ********************/ 
 nrfx_timer_t main_loop_tmr_inst = NRFX_TIMER_INSTANCE ( 24 ); // enabled in prf....conf 
 
 /* Define the IR LED timeslot interval */ 
 #define MAIN_LOOP_TMR_INTERVAL_US 100 
 
 uint16_t tenth_sec_count = 0 ; 
 uint16_t tenth_ms_count = 0 ; 
 
 /* Implement timer callback handler function */ 
 void main_tmr_cb ( struct k_timer * timer ) 
 { 
 tenth_ms_count ++ ; 
 
 setGPIO (DEBUG_OUT,tenth_ms_count % 2 ); 
 
 if (tenth_ms_count > 999 ){ 
 tenth_ms_count = 0 ; 
 tenth_sec_count ++ ; 
 } 
 } 
 
 /* Define the IR timeslot timer instance */ 
 K_TIMER_DEFINE (main_loop_tmr, main_tmr_cb, NULL ); 
 
 void configure_main_loop_tmr ( void ) 
 { 
 nrfx_err_t err; 
 #if defined ( __ZEPHYR__ ) 
 IRQ_CONNECT ( NRFX_IRQ_NUMBER_GET ( NRF_TIMER_INST_GET ( 24 )), IRQ_PRIO_LOWEST, 
 nrfx_timer_22_irq_handler, & main_loop_tmr_inst, 0 ); 
 #endif 
 
 /* Declaring timer config and intialize nrfx_timer instance. */ 
 nrfx_timer_config_t timer_config = NRFX_TIMER_DEFAULT_CONFIG ( 1000000 ); // 1MHz 
 err = nrfx_timer_init ( & main_loop_tmr_inst, & timer_config, NULL ); 
 if (err != NRFX_SUCCESS) { 
 printk ( "nrfx_timer_init error: %08x" , err); 
 return ; 
 } 
 
 /* Set compare channel 0 to generate event every MAIN_LOOP_TMR_INTERVAL_US. */ 
 uint16_t timer_ticks = nrfx_timer_us_to_ticks ( & main_loop_tmr_inst, MAIN_LOOP_TMR_INTERVAL_US); // 10kHz 
 
 nrfx_timer_extended_compare ( & main_loop_tmr_inst, NRF_TIMER_CC_CHANNEL0, timer_ticks, NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK, false ); 
 nrfx_timer_enable ( & main_loop_tmr_inst); // enabled with "true" flag in nrfx_timer_extended_compare 
 k_timer_start ( & main_loop_tmr, K_NO_WAIT, K_USEC (MAIN_LOOP_TMR_INTERVAL_US)); 
 
 }

NRF54L15 Timer running much slower than expected

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