Question: I have been working on a project in which I need to connect to a BLE and communicate with Arduino through BLE. Every thing worked fine until I update my device to Android M. I haven't changed anything in my project but now my app not connecting to BLE.

Answer: 
I also faced this problem. All you need to do is to enable *ACCESS\_FINE\_LOCATION* & *ACCESS\_COARSE\_LOCATION* 
permission in your manifest and also you need to enable location service(by turning on GPS).
Android M needed GPS should be on for effective working of bluetooth, that's why it is unable to connect to android BLE. Give GPS permissions also. Hope it will help