tl;dr Hold down space bar when you jump to safely deploy your glider.
If you’re having trouble opening/closing the glider when you jump, just hold down space when you jump, the glider will auto deploy as soon as possible. Once it is deployed you can release the spacebar and the glider will still be deployed, you can then control it further from the gliding state. I have found this to be a much more consistent way of deploying the glider when jumping.