My sixth glider was somewhat similar to what you're describing. I viewed his personality as the most scared or nervous, which meant he needed a lot of patience and for me to give him the time he needed to become comfortable. I made sure to always play with him in a tent so I wouldn't have to ever chase him (and make him even more nervous) and always had his favorite pouch and some treats ready for him when I needed to get him back in the cage. I've had him about nine months and he's still a bit skittish but also came a long way!