I have a HTC one,sometimes for some ungodly reason it will not connect I have to go into the bluetooth settings and touch the Hyundai pairing to connect it,then from then on it connects automatically,I think it is more a glitch in the phone not the car.
If it continues to be a problem,once I deleted the phone from the bluetooth menu in the radio(instructionc in your manual)also deleted the car pairing from the phone and started from scratch,this also fixed the problem for some time,the HTC phones are OK,but sadly they are not as reliable as HTC quotes and once they have a bit of age and use,they can be tempremental.