Pascal Gross' controversial injury-time penalty rescued a deserved draw for Brighton although Liverpool still went top of the Premier League.
It was Brighton's second penalty of the game after Neal Maupay fired a first-half spot-kick wide at the Amex Stadium.
The Reds thought they had taken the lead when Mohamed Salah latched onto a Roberto Firmino ball before firing home, but it was disallowed for offside by the video assistant referee.
Diogo Jota broke the deadlock, with his ninth goal since joining the Reds, as he received Salah's pass before going past two defenders and firing into the bottom corner.
Substitute Sadio Mane believed he had sealed the game with a late header for Liverpool but that was also ruled out by the VAR for offside.
And they were made to pay when Andy Robertson kicked Danny Welbeck's boot - with Stuart Attwell awarding the penalty after viewing the screen - and Gross slamming the equaliser down the centre.
Henderson later said: "It was ours. It should be three points, in my opinion. I've seen the replay. Who would be happy? It's not a pen. It feels like we're standing here every week and discussing incidents. I don't want to get into trouble, but for me it's not a penalty.
"Danny Welbeck said to me it wasn't a penalty. There were four or five of them who felt it wasn't a penalty. To overturn it, it has to be clear and obvious. Is that a clear and obvious penalty, to go to the screen and overturn it. Obviously the referees know better than us, but I thought the lads were brilliant today and deserve the three points.
"In the first half there were things we could improve on, in the second half we did that. We had a couple of goals ruled off for offside. Overall we've got to be positive and take the performance out of it, because the result isn't anything else but an error in my option. You'd rather get beat by two or three than end up like that. It feels like two points taken away from us."