I had a male Phyllovates chlorophaea (TX Unicorn) that was like this. He died this morning. I had two mature females and he wouldn't mate with them. One was very tolerant of his strange antics. He would get on her back and often grab one of her arms. She was usually eating during the mating attempts. He would change positions frequently, making small adjustments for unknown reasons. She was VERY eager to mate, but he just wouldn't hook up. He lived for 3 months and I attempted matings just after his feedings. He never seemed to bite at her, but he would just thrash on her and even grab her head sometimes. I left them together overnight once when I was just frustrated with him. He was on the other side of the cage in the morning. I'm very skeptical they ever mated. I couldn't believe she never ate him just out of spite.The other female had no tolerance for him and tried to attack him a few times.
It seemed like he tried to hook up a few times. Between the familiar movements of his antennae and the circular motions of his abdomen, it appeared he wanted to, but was suffering from some kind of "performance anxiety".
This is the only time I've ever seen a male this confused (and a female this tolerant). He showed so much interest in being on her back, but never completed the act.