The island is supposed to be the same island they were shipwrecked on. However, both as an uncharted island and as a resort, it is clearly much larger than the original island.
While the island as a resort could easily be a port-of-call for cruise ships, as it was in the movie, it would be highly unlikely people would be delivered to the island from a cruise ship for a stay of any number of nights. For that reason, the island should have its own chartered planes from Honolulu that can bring people to and from the island.
The tidal wave apparently contaminated the aquifers on the island with salt water, but the castaways have been there for at least 12 days (according to the radio report on them) and the Minnow II was completely lost at sea, so they brought no water with them to the island. The average human being can't go without water for anything beyond three days at best, and combined with the climate of a tropical island in the South Pacific, the castaways would all have died days before. Yet, up until the start of the movie, they've apparently gone on with their routine without a worry. It's possible they subsisted on coconut milk in lieu of fresh water.
Gilligan clearly jumped out of the plane with Mrs. Howell's suitcase, when he was supposed to have fallen out after throwing it out.
As Gilligan is chasing the boy, gymnastics parallel bars are clearly seen among the trees and brush (which the boy does actual gymnastic moves off of, something that would be almost impossible to do on tree limbs).
The backstory over how the WW2 planes and hangar were found was that the tidal wave that hit the island and helped them get off and rescued removed enough brush that they were both exposed. However, there was still enough growth and brush on the planes that needed to be removed, and secondly, in 15 years on a tiny island they would've eventually, sooner or later, have come across them.
Unlike the first Minnow, the second Minnow was lost completely at sea, so how did the castaways have any luggage or any other change of clothes with them, as shown on a clothesline and when they were throwing luggage out of the plane.
The only boat that was shuttling guests between cruise ships and the island was the Minnow IV, so Gilligan and the Skipper should have already known about Robbie's parents before they got to the island. Otherwise, how did they get to the island to look for Robbie?
The Professor said that he'd have to "feather engine 1" (shut down), but he shut down engine 2. Engines are labelled from left to right.