Before practicing for the karaoke contest, in their room, Rachel wears a striped tank top plus a golden necklace, while Harry wears a red shirt with white leaves on it. When they are on the scene, Rachel has a striped T-shirt and Harry has a gray shirt with white flowers, but in the next moment she has again the striped tank top (without the necklace) and he wears the red shirt.
At the ash-spreading scene outside on the deck, views of the characters from the deck out towards the sea are very windy, showing Harry and Rachel's hair blowing fairly strongly. But the same scene's views from the sea in towards the deck are calm, with Harry's hair very tidy.
When Rachel describes that the Pina Colada song is about cheating, she mixed up the story. She said that the husband puts an ad in the paper and the wife responds to it because she is also thinking about cheating. It was actually the wife who put the ad in and he responded to hers.
Harry and Rachel would not have been permitted to board if they were that intoxicated.
Cruise lines will not allow a last minute passenger substitution. Honeymoon Suite is not a category on Harmony of the Seas and Harmony in 2018 is sailing out of Florida.
In scenes where the camera shows the boat, it is travelling north instead of south like it should be. This is known because of the direction of the sun.
We see Harry and Rachel seated at breakfast with their "designated table mates", and it is implied they are in the buffet (Windjammer), but the scene was filmed in Costal Kitchen which is exclusively for suite guests.
At the beginning of the film, the wedding board date announcing Rachel and Owen's wedding says September 9th, 2018. The cruise that Rachel was supposed to go on occurs two days after the wedding, yet while on there - Harry's phone rings and the date reveals to be Sunday, February 18th.
After their drunken evening, Rachel and Harry arrive on the cruise unpacked and empty-handed apart from their donned clothing - forcing them to shop for new ones. Yet later, Dad mysteriously has the ashes of his dead friend with him.
In the formal night scenes, both Harry and Rachel are wearing formal wear. Harry's tuxedo can be explained because tuxedos can be rented on board most cruise ships. That doesn't explain how Rachel got a formal gown if they came on board with no luggage.
Cruise lines will not allow a last minute passenger substitution. Honeymoon Suite is not a category on Harmony of the Seas and Harmony in 2018 is sailing out of Florida.