USART interrupt handler is invoked only once

Kernel
13

NVIC_SetPriority is mapped to __NVIC_SetPriority

If you see below implementation the priority value is getting shifted.

 NVIC->IPR[((uint32_t)IRQn)]               = (uint8_t)((priority << (8U - __NVIC_PRIO_BITS)) & (uint32_t)0xFFUL);