The real reason this "antisemitism in the Labour party" ****** has dragged on for so long is because it isn't really about antisemitism in the Labour party, it is about removing Corbyn and his acolytes from the leadership of the party.
Corbyn was considered a joke when he took over the Labour party but he isn't considered a joke any longer, although he may be despised by the media and a lot of the PLP he still has strong support from the membership, so the prospect of him being removed by the grassroots supporters looks remote.
If Corbyn remains leader of the Labour party there is a possibility he could become prime minister and you only have to look at his policies to see the danger, he would recognise Palestine and ban weapon exports to Israel and Saudia Arabia which would wind up the Israelis and Arabs no end.
Domestically he says he would tax the rich more which will cause extreme consternation among the tax dodging community,also he has pledged to allow in even more migrants and asylum seekers which will windup the Daily Mail readership and Tommy Robinson.
With all the above it is not surprising that there is obviously a concerted effort by his opponents to remove the possibility of him ever getting his hands on the levers of power.