1. Pro-Israeli groups and politicians who want to force Labour back in line on the Israeli-Palestinian issue.
2. The Tories, to smear their opposition.
3. People within Labour who want to just the more left-wing Corbyn.
The more you read about these "antisemitic incidents," the more ridiculous it gets. One perfect example was the Jewish Labour member who was accused of antisemitism because she said Holocaust memorial day should be used to remember all genocides. There was a concentrated effort to smear her as an antisemite, despite the fact that she's Jewish, and that there's nothing remotely antisemitic in what she proposed.