Since yesterday's patch, the pull up skill on the Griffon mount does nothing anymore during dives. This basically means, that you have no way to cancel a dive and pull up early and also need a much higher starting point to speed up your Griffon. People who learned how to control their Griffons properly with its pre patch movement mechanics now hit the ground left and right because of this.
According to this reddit post, the change was intentional/part of a bug fix.
In my eyes though, the current behaviour is buggy and should get the attention it deserves. This changes the previously fluent (=fun) movement behaviour of the Griffon into a clunky mess. In other words: somthing that did not feel broken before, now does.
You had created such a great movement experience with the Griffon, but this patch broke it for many of us. Please revert this.
EDIT: Changed wording based on a comment of @Illconceived Was Na.9781 - hope this is better
another EDIT (08.02.2018): The change is now documented in the late patch notes and the problem regarding the pull up button not doing anything at all during a dive was apparently fixed in a hot-fix patch. There is now supposed to be an 800ms delay for pull ups during dives, but according to some players the actual delay appears to be higher than that. I will test this myself once I get home though.