In timer OSAL, the timer reset is done last after all initialization including the interrupt registration is done. This triggers interrupt even when timer is initialized in TimerP_StartMode_USER mode.

Interrupt would be triggered due to earlier timer initialization -

1. SBL uses timer 0 and keeps it initialized.
2. The app comes and uses timer 0 with USER mode
3. Due to earlier configuration of timer, the interrupt gets triggered.

below is called

/* Register interrupts */
(void)Osal_RegisterInterrupt(&interruptRegParams,&(timer->hwi));

before

/*if doing soft reset: do it first before setting other flags */

if ((timer->tiocpCfg & TIMERP_DM_TIOCP_CFG_SOFTRESET_FLAG) > 0U)