When triggering glide with the umbrella, sometimes it will only produce the sound but not glide. By the time you notice this, chances are, you fell too far already and need to climb back up.
I've reported this before the wipe already. Does not appear to have improved and the post is gone.
Also have seen this frequently, especially while using 1h weapons like knife or sickle alongside the umbrella. I tend to do a lot of landscape traversing by jump off small rises, forward dodge, pull glider to get some extra distance. It might be latency or load time/framerate related - happened fairly often while running the game off HDD rather than SSD.