To go a bit more in depth about this, which I’ll show with some screenshots in just a second, when a druid is in Flight Form in the air, you can net them just fine. If they’re in Flight Form touching the ground, you’ll be met with a “Invalid Target” error and can’t even cast the Net-o-Matic. If they’re in the air and you’re casting it on them, and they touch the ground while you’re casting it, the net will go off but have no effect.
Successful cast 
https://i.imgur.com/pEiUCpc.jpg
Unsuccessful cast 
https://i.imgur.com/ikup2Ry.jpg
The first screenshot is the Net-o-Matic working successfully, while the second screenshot is the Net-o-Matic cast going off, but working unsuccessfully as they touch the ground.
This used to work on Druids before their forms got consolidated into one spell, aka Travel Form. The spell is supposed to dynamically change their form depending on where they’re at, such as if they are in the water while in Flight Form it’ll automatically switch to Aquatic Form, once they’re out it’ll automatically switch to Flight Form, etc.
I think what’s happening is druids are being recognized as a ground mount while in Flight Form, however they still can jump off and fly like any other flying mount. The Net-o-Matic only works on flying mounts and therefore, because its doing this, just ends up taking zero effect on them. Please fix!