I know this is FIFA VAR room but did none of these, whether referees or technical support spot the lines were not drawn on the second to last defender, it was fairly easy to see with one look.
It is reported John Brooks drew the wrong lines, but wouldn’t it make sense for a technical expert to draw the lines for John Brooks and he then uses his refereeing expertise to judge whether it is offside or not?
Multiple offside checks by technical experts can be made simultaneously so that the Lee Mason error isn’t made in the Arsenal match.
Mason, Swarbrick and Dean are full time VAR specialists, training and practicing all week.