Video assistant referee operator Lee Mason did not draw the VAR guide lines to check for offside on Brentford's equaliser against Arsenal on Saturday.
Ivan Toney's goal was the subject of a VAR check by Mason following Ethan Pinnock's challenge on Gabriel.
That incident was cleared but there was a suggestion Christian Norgaard was offside in the goal's build-up.
However, Mason did not use the system's lines that would have shown whether the Brentford man was offside or not.
The incident is being put down to human error.
Arsenal manager Mikel Arteta accused officials of "changing the rules", while former Liverpool midfielder Danny Murphy called it a "horrendous decision".
"I just looked back and it is offside, yes," Arteta said after the match.
"You have to apply certain principles in defending and you do that by sticking to the rules. Suddenly you change the rules and then you have to change your principles.
Human error was also blamed for Brighton having a goal incorrectly ruled out in their draw at Crystal Palace.
It adds up to an uncomfortable day for new Premier League referees chief Howard Webb, who has pledged to drive up standards in the top flight.
Webb's early weeks in the job have been regarded as positive. However, for Mason, a dedicated VAR official, to be involved in one of two key mistakes on one day, creates a difficult situation for Webb to deal with.
