First - note the correction to my post above!
If both tasks are the same priority, then a higher priority task won’t be unblocked, and it would be expected that *pxHigherPriorityTaskWoken remains pdFALSE.
Interrupts that call API functions must be at or below the priority set by configMAX_SYSCALL_INTERRUPT_PRIORITY (some ports call this configMAX_API_CALL_INTERRUPT_PRIORITY) - how to configure that depends on the port you are using. configKERNEL_INTERRUPT_PRIORITY should always be the lowest interrupt priority there is. There are several pages that document this, including RTOS for ARM Cortex-M