Probably me being dumb but.....

I have maxed out all the masteries for the Griffon mount..

I see players flying around with ease, and hovering etc. and my Griffon just drops like a stone and can't ever get any height, even with Bond of Vigor running. I read something somewhere about a 2nd ability bar (blue), but I only have the standard one above the Heath Globe, that drains pretty much instantly when I press space.

Please help :((

I think what you saw wasn't the griffon mount but the Skyscale mount instead. The Skyscale is the only flying mount that can hover and stay in the air while the griffon can't. It is also the only mount with a "blue 2nd ability bar" which indicates the altitude it can reach. However you can also gain height pretty easily with a griffon if using the dive from a high point which makes it faster and when it's fast enough you can pull yourself up to gain more height.For more info about the Skyscale check: https://wiki.guildwars2.com/wiki/SkyscaleI hope that helps.

The griffon masteries will help you stay aireborne longer, but only by moving faster - if you use the swoop and wing flap abilities while diving you can then climb higher than your starting point, and when you're gliding after diving you go faster and lose height at the same rate so you can go further before landing. But none of them make it possible to hover or give you better control, so that definitely sounds like the skyscale.

As mentioned before, that was a skyscale, not a griffon. The griffon requires height in order to gain insane speed (with mount skill 2) and reach higher heights than normally. The skyscale can never get close to that speed, but can gain height more easily.

Mount skill 2 cannot be found in your skill bar, by the way - you have to assign it manually in the game's keyboard settings.