I had this similar thing happen while farming timbermaw. I somehow lost two of them on my main, separate pc. Everytime I made the circuit, there they were. According to them, they were with me the whole time. They got xp and looted and attacked as normal, so I went with it. Finally flying away fixed it up. I noticed when I did the 2box on epic flying, the one pc would say it was next to my main, but my main disagreed, saying the follow toon was far away, would always break follow. It seemed to work fine on normal flying. I got into the habit of braking every few seconds to allow my main to recognize the follow was right behind me, annoying and made the cost so worthless at the time.