It's a particular problem in the UK among supporters of the Left wing opposition party led by Jeremy Corbyn. Dave Rich has written an excellent book on the topic - 'The Left's Jewish Problem'.
The left have were traditionally supporters of Israel. Then they began to define themselves in terms of support for the 'oppressed minority'. Israel began to be equated with the Apartheid movement in South Africa and Palestine became the cause celebre of western socialism.
They hide behind the lie that they only oppose Zionism and not Jews but when you dig into the journals and books intended for socialist audiences it is obvious that anti-zionism is nothing but a veil for Jew-hatred.
Incidentally I have never spoken with a conspiracy theorist who was not also an anti-semite.