I have OCD for compiler warnings... I must use -Wall (I'm a freak like that).
In nrf_drv_twi.c line 433 there is a function twi_clear_bus. This gives an -Wunused-parameter warning.
If you add
static void twi_clear_bus(nrf_drv_twi_t const * const p_instance, nrf_drv_twi_config_t const * p_config)
{
(void) p_instance; // new code
NRF_GPIO->PIN_CNF[p_config->scl] = SCL_PIN_CONF;
...
Then the warning goes away