The only thing I can think of with the Dunk one is that he had been made aware of / was aware of Dunk's cheeky step on Romero's toe immediately beforehand (the one that made him go down in absolute agony) and had that in the back of his mind. I know two wrongs don't make a right - but maybe it was a sort of 'you got away with that one, so I'm not giving you anything for this one'. Otherwise....I don't know.There are two different questions being asked here.
The thread title asks about the worst ref decision. The poll asks about the worst decision, which I'd take as being a combination of ref and subsequent VAR.
So, for me the worst *REF* decision was the Dunk non-penalty.
Attwell, to his credit, was pretty much perfectly-placed for both big penalty shouts, but we know he gave neither. I'm pretty much always willing to forgive an on-field ref for getting it wrong as they have a split-second single-angle full-speed view of top-class athletes who spend the entire game trying to con them.
So, I could see how he may not have given the Mitoma penalty in real-time.
I don't see how he could have missed the blatant two-handed pull on Dunk's shirt as he attempted to run onto an incoming cross. There's no player fakery possible there, it's obvious and blatant.
However, once you bring VAR into play, ie taking a more holistic view of a decision, then the Mitoma one is equally unfathomable. The VAR official would have had time to review multiple angles at multiple speeds, pretty much all of which would have shown it was an obvious foul. How he did not intervene is almost impossible to understand.