nRF52832 SAADC and NUS over BLE not working at high sampling rates

I'm using an nRF52832 on a custom board but developing its firmware on nRF52-DK (so there's no hardware issue).

I'm measuring a voltage using the SAADC and send it over BLE. I used the "ble_app_uart__saadc_timer_driven__scan_mode" example, but I have changed the default sampling rate from 250ms (4 Hz) to 2ms (500 Hz), and increased the ADC samples in buffer from default 4 to 12. This is causing loss of data, as well as occasional disconnecting. 

The datasheet of nRF52832  says that the ADC can sample at frequencies as high as 20kHz and the BLE can send data at 2MB/s. 

Can anyone please help me understand what I'm doing wrong?

Any help will be much appreciated. Slight smile

Thanks in advance.