Perception is important, but after 4 years of an orchestrated campaign by political opponents inside and outside the Labour Party, and the vast majority of the press and UK media (especially the 'liberal' media led by the Guardian and BBC) it is little wonder that those numbers came up. At the same time the general public thought that over 35% of Labour members (35% of 550,000 +) had been accused of anti-semitism. The actual figure was 0.1%. And many of those accusations were inventions - or were far right social media posts falsely attributed to Labour members. Many more were for the 'new anti-semitism' (invented in the 1990s) of opposing the political ideology of Zionism (especially by calling it inherently racist), opposing illegal settlement expansion and war crimes by Israel, supporting non-violent resistance to ethnic cleansing at the request of Palestinian civil society organisations, like BDS, claiming that the anti-semitism crisis in Labour was exaggerated, and even in a few cases of advocating a 2 state solution to Israel-Palestine in line with the UN and most world governments. A high proportion of Labour Party members charged with these 'crimes' were (and are) Jewish.
Corbyn was a disaster in dealing with 'the crisis', in large part because he constantly demonstrated his political pacifism by not standing up to it - by clearly identifying the real examples of anti-semitism (hatred of or discrimination against Jewish people) of which there were some, but explaining and rejecting the false allegations. He avoided conflict, offered compromises (where there should have been none), and eventually tried to paint himself as a more effective witch hunter than the Labour right. A doomed and flawed strategy that set back the fight against racism (especially anti semitism) for years and handed the Labour Party to Starmer. 200,000 members left (to the joy of the Starmer clique), the Forde report was ignored, the Board of Deputies retained its veto over parts of Labour's internal policy and membership rules, and the front bench fell over themselves to announce they were all-in Zionists.