The Premier League's Key Match Incident Panel felt Gabriel Martinelli fouled Mats Wieffer right at the end of the first half at the Amex recently.
Arsenal went on to complete a 1-0 win on a night being seen as potentially key in their progress towards a probable Prem title.
They ground out victory while rivals Manchester City were drawing with Nottingham Forest.
The penalty appeal was largely overlooked at the time as focus was turned on complaints about Arsenal’s time-wasting tactics.
But Albion head coach Fabian Hurzeler said on TNT Sports he felt it was a penalty
Now the KMI Panel have said they reckon Mikel Arteta’s men got away with one.
Referee Chris Kavanagh allowed play to continue and then delayed the half-time whistle as he awaited guidance from his video assistant Michael Salisbury.
Once the incident had been cleared, Kavanagh blew for the interval amid boos from home fans – although this seemed at the time to be because he had not allowed the home side to take a free-kick they were waiting to deliver.
But the KMI Panel voted 4-1 that a spot-kick should have been awarded on the field and 3-2 that it was a missed VAR intervention.
They reported: "Martinelli is not looking at the ball, holds Wieffer into the area and prevents the Brighton from challenging for the ball."