It depends on the vehicle you attempt to put a locking gas cap on. It can mess with components of the “anti-pollution” system. I had a Dodge Caravan in California and it would blow a pump out within a day when I put on a locking gas cap.
Had this happen to me. Use to Van pool to work in a large 12 person van. We filled it up on Friday and left it in the park and ride. Somebody drilled a hole in the tank and bailed. Received a call from the police, the parking lot was covered in gas and the fire department had to do a clean up.
I don't think a locking gas cap has anything to do with fuel system failures. The gas cap was unlikely to be compatible with the car. I just had an engine check light come on a week or so ago. I checked the car's manual and the top reason for the alarm was the gas cap. I inspected the gas cap on my 13 year old car and sure enough the O ring was high degraded. I went to an after market parts store and paid $15 for a a gas cap that was compatible with my car. Problem solved.