A glitch affecting a single computer monitor is responsible for the sudden canceling of the CNN/Des Moines Register poll — the pivotal ranking of Iowa’s Democratic presidential candidates that had been set to drop Saturday night just two days before the state’s caucuses.

The highly anticipated ranking, set to be released at 9 p.m., was spiked at the last minute after the error was discovered by the campaign of candidate Pete Buttigieg, according to a source familiar with how the poll was conducted and produced.

Pollsters found that the computer monitor — one of the “many dozens” used for live telephone surveys — was set with a font size that was too large, the source said.

The erroneous setting meant only 11 of the then-12 candidates’ names fit onto the screen, which was accessed by telephone surveyors asking Iowa Democrats about their preferred next president.

At least one of the poll surveyers happened to dial a Buttigieg supporter — and, due to the glitch, inadvertently failed to mention the candidate’s name.

The supporter raised a red flag to the Buttigieg campaign, which called the pollsters, leading to the discovery that spiked the poll.

“While this appears to be isolated to one surveyor, we cannot confirm that with certainty. Therefore, the partners made the difficult decision to not to move forward with releasing the Iowa Poll,” wrote the Des Moines Register.

The pollsters didn’t learn of the issue until Saturday, the source told The Post.

The computer monitors randomly generate names for each call a surveyor makes, meaning the setting could have chopped off different candidates’ names for different calls, the source said.

But pollsters by Saturday were only alerted to the one call placed out to the Buttigieg supporter.

“A respondent raised an issue with the way their interview was conducted, which could have compromised the results of the poll,” CNN said in a statement.

The paper has published the poll — conducted by polling firm Selzer & Co — for 76 years.

The backpedaling caused CNN to drop an hour-long special on the results.

“We were unable to ascertain what happened during this respondent’s interview, and cannot determine if this was a single isolated incident,” CNN said in a tweeted statement.

Recent polls have shown a tight race with Bernie Sanders gaining steam in a neck-and-neck race against Joe Biden.