There are several pieces of art on Lizzie's wall that are clearly beyond her skill as an artist. Where'd those come from?
In Fairy Dust & The Quest For The Egg, Captain Hook cannot see the fairies because he is an adult. (According to Gail Carson Levine adults cannot see fairies.) Whut? A major plot point in Disney's continuity depended on adults being able to see fairies - it was Tinker Bell who betrayed the location of Peter Pan's hideout to Captain Hook, and he obviously had no trouble seeing her.
In Tinker Bell and the Lost Treasure, when Tink doesn't get her daily ration of dust, she's stuck with walking. In Tinker Bell and the Great Fairy Rescue, not only is she still able to fly after a day without her ration, she has enough to spare to let Lizzie fly.
Possible Fridge Brilliance? Isn't it said/implied at the end of Lost Treasure that this is one of the largest amounts of pixie dust to be made at one time? "Over a million smidges IIRC". Maybe because there's a little extra, the fairies going to the mainland get extra pixie dust since they're going to be leaving Pixie Hollow.
Why is the art in this so.. good compared to other CGI productions, especially for this demographic? Did someone dig up the Peter Pan artbooks or something? There's none of the typical major facial deformity utilized in everything else done in CG since ReBoot (Tangled aside, maybe it's a Disney thing?)
John Lasseter is the exec producer of all the Disney Fairies stuff. That tells you everything you need to know.
What is the explanation for the ice fairies being at Tink's birthing ceremony? Did they just not think of that plot point yet?
Considering Tink, Bobble, and Clank fly over the Winter section of the Hollow before Tink is ever shown where the Tinker Fairies live, no, they had not thought of it yet. They have no problem other than getting a little chilled, and the overseer of Winter is allowed to go to Pixie Hollow without repercussions, even though she's in the spring area most of the time where we see her. This should have been bad for her, since she's so adept and presumably reliant on the cold. It's also possible that sometimes fairies get sent to the wrong places in the Hollow, so fairies with Winter talents attend the birthing ceremony just in case of such an event.
Why can't they fly with wet wings? The dust that they use has lifted things much heavier than them before, some added moisture shouldn't effect it that much.
Maybe it's not about weight, but about aerodynamics. Like the way airplanes have trouble flying with ice on their wings because it messes up the shape of the surface and therefore the airflow.
Not to mention that maybe they're simply harder to move when they're wet, which makes it almost impossible to fly.
If humans who are much larger than fairies and have no wings can fly if they have pixie dust, and fairies' wings are basically useless since they can't fly without pixie dust, why can't Rani fly?
Humans are more used to walking and running and generally getting around on two feet, so they can push off of things with less difficulty (they're more floating than flying). Rani might not have the strength to push herself around. Or nobody even thought of that. It could have to do with the fact that Rani is made from a laugh, and humans, well, aren't. Or maybe Neverland's messing with physics, and Rani can't, and doesn't necessarily want to leave, and she would be able to fly on the mainland.