Yeah. This invasion is super bugged. The ONLY way to break out of that midair state is to click on a multiperson mount like a yak, have said friend/random run off the cliff, survive, and drag you to the eagles that fly you up to the legion ship.
I’ve gotten stuck on my demon hunter before. Even if you dash or slam your way to the nearby hill - you will be stuck unless you do what was posted above, or wait for the scenario to be completed if you’re just that unlucky.
THIS IS A BUG THAT NEEDS TO BE ADDRESSED AND FIXED. (Especially if you use these invasions to power level through Legion!)