Yes, I read a book about this.
The author's theory was that in the mind of the 'anti racist' you can't be racist to Jews because people understand racism to be a general prejudice based on perceived inferiority, whereas left-wing antisemitism tends to be the opposite.
Many will deny Jewish is a race, which further prevents them from recognising racism, but then physical characteristics are used to form racist characatures of the Jew with a hooked nose and so on.
Most left wing antisemites think Jews are white, ignoring that many are not, and indeed that 6 million of them were mass exterminated recently based on the theory that they were not white.
As Jews are not perceived to be economically disadvantaged, and are seen as unusually successful and highly represented in power positions, left-wing antisemites find it impossible to recognise their own racism.
Add on to that, antisemitism is more like a conspiracy theory or mass bullying than racial supremacy in left-wing ideology. They don't think Jews are inferior, they just think they're collectively evil based on a wide range of antisemitic propaganda they've consumed.