The data value was sent to the mobile phone in hexadecimal using the function ble_nus_string_send.

[Aser]

Hello, Guys.
Using the function ble_nus_string_send,
I've sent sensor values to my mobile phone.
However, the data received came from an unknown character being broken.
I'll attach the picture as well

Why is my sensor so broken that it is transmitted?

[Edvin]

Hello,

In the log vies (where your screenshot is from), it is trying to print the received messages as ASCII values. If the values aren't ascii values, it will print these question marks. You can see the hexadecimal values above the "??" in your screenshot as well. 

So this is not a bug, it is just how the app displays the received data.

Best regards,

Edvin