Rayo Vallecano were left seething as a VAR failure meant Lamine Yamal's first-half penalty could not be reviewed during Sunday's 1-1 draw with Barcelona.
Yamal converted from the spot in the 40th-minute after colliding with Pep Chavarría, with Rayo's players convinced the decision should have been overturned.
However, MEDIAPRO, the company who administers VAR in LaLiga, confirmed after the game that the technology was not working in the first half at Estadio de Vallecas.
"A technical problem, the causes of which could not be determined, prevented the proper functioning of the VAR service during the first half of the match between Rayo and Barça," a statement from MEDIAPRO said.
"Despite the efforts made by the entire technical operations team, it was not possible to properly restore the service during the first half, but it was reestablished and functioned normally during the second half.
"MEDIAPRO is working to clarify the causes of the incident."
Yamal's penalty put Barça 1-0 up and led to furious scenes on the sidelines as Rayo coach Iñigo Pérez contested the ruling.
"I'm ashamed of my reaction on the touchlines after the penalty was awarded," Pérez said after the game in an interview with broadcaster DAZN. "It was the result of frustration. Referees make mistakes and that's OK. What bothers me is that today the players had five minutes of VAR and five minutes without it and so on.
"Everyone that's played knows the influence it has on the players, referees and assistants now... It's a different game.
"Maybe it's a penalty, I don't know, but it's not fair that players and officials aren't protected. I'm annoyed by the lack of efficiency with these things."
Pérez also conceded the issue could have been "our club's fault" as he suggested games should be halted if VAR fails in the future.
"We need better protocol for these situations," he added. "My anger is over the lack of protocol and the lack of efficiency.
"It's not a good image for our league. If VAR is not working, we should suspend the game until it is."
Rayo forward Isi claimed referee Mateo Busquets Ferrer told the players he had made a mistake in awarding he penalty to Barça.
"When they give a penalty that isn't a penalty, it makes you angry," Isi told DAZN. "I could say a thousand things right now, but [the referee] is human and he makes mistakes too.
"He told me he accepts it was a mistake, so fair play to him. Without VAR, it's very difficult to referee. So I'm going to bite my tongue. It's to his credit as a person that he admits his mistake."
Rayo fought back from the setback of going a goal down to draw 1-1 against the Spanish champions, Fran Pérez earning them a point with his first goal for the club in the second half.