A review has been ordered by racecourse bosses after all but one runner was disqualified from a race at Fontwell.
Dharma Rain was awarded Sunday's race, having crossed the line in seventh.
The first six horses to finish all failed to jump the third-last hurdle as jockeys were left confused, with groundstaff appearing to indicate it should be avoided.
Arena Racing Company (Arc), which runs Fontwell, says it is looking into the incident.
"Arc are in the process of undertaking a full review of the procedures that were adopted to guide runners around a horse receiving veterinary treatment," it said.
"Regardless of the outcome of this investigation, as a goodwill gesture to the owners of the horses that were subsequently disqualified, Arc will pay the equivalent of the prize money to the first four horses past the post."
Groundstaff appeared to be in the process of dolling off the flight while a flag was also being waved.
However, as the markers were actually behind the hurdle, the rules state it still should have been jumped - as Jack Tudor did on Dharma Rain.
It was the third racing controversy in three days.
Officials at Cheltenham will consult with the British Horseracing Authority to see if anything can be done to prevent a repeat of the light issues that affected the final race on Saturday's card.
The closing mares' bumper was staged in murky conditions and following a thrilling finish, a dead heat was called between Harry Fry's Ishkhara Lady and the Dan Skelton-trained Elle Est Belle.
However, the dwindling light at the course made the official photo hard to read, prompting some outcry about the result on social media.
On Friday, initial winner Twin Star was disqualified after conditional jockey Alexander Thorne failed to weigh in at Taunton.
Because of Covid-19 protocols, jockeys at the Somerset track are currently using a temporary changing room, while the scales are in their usual spot.
Thorne went directly into the changing room after conducting a winning interview rather than weighing in first.
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