Viewers accused the pair of pretending to be together for convenience as the TV special came just days after Dani told fans they had split – only to rekindle things a few days later.
Fans were suspicious of the pair during the show, especially as filming took place a short while before they temporarily ended things.
One wrote: "Jack and dani still kiss like 10 year olds #LoveIslandReunion."
Another said: "Dani and Jack are so annoying??and they kiss like some awkward 15 year olds first time #LoveIslandReunion."
Others claimed they were "forced" and merely together for the money.
One ranted: "Jack and Dani are fake goals #LoveIslandReunion."
Another said: "Wait and see, I bet once @Dani_MasDyer & @jack_charlesf have been paid for this #LoveIsland Christmas Reunion, they won’t be together. #Bores #Fakes."
Someone else added: "I don’t believe in jack and Dani. It’s all forced #loveislandreunion."
Fans were also baffled by the couple's very different standpoints on Georgia Steel and Sam Bird's split.
Jack was very much team Sam, and even called Georgia "a liberty" when she claimed Sam had been mean and "trapped" her during their relationship.
Despite admitting she was at her boyfriend's house at four in the morning, Dani insisted she believed Georgia's denial that she cheated.
She said: "I don't think she cheated. She looked me in the eye, as a friend, and said she didn't…"
However viewers were quick to point out that Georgia also promised Dani that she hadn't made a move on Jack Fowler during their date in the villa – which was later revealed as a lie.