I have had issues where my glide only activates for like a split second before canceling. this still happens if I log out and try again.
What’s your ping like? Sounds like lag.
I have had that happen when I use the jump key to activate Glide. If you are falling, the first press of jump activates Glide and the second press deactivates it. If you jump and are still rising, the next press of jump causes a second jump, and the following press of jump activates Glide. So, if you are falling and press jump twice, you activate and immediately cancel Glide. If you are rising from a jump and press jump twice, you activate Glide. Could that be what you are experiencing?