I briefly re-joined Labour under Corbyn - but had a rude awakening when he simply failed to stand up against bullying and intimidation in the party; especially in local CLPs. He'd be at meetings when a candidate or MP was being treated and spoken to appalllingly - yet he never once called it out. I lost all respect for him then. I thought he had honour, and principles - he does, but they are all ideological.
Anti semtism is not as simple as being prejudiced just because someone is jewish - a lot of it has far deeper roots and now manifests in automatic prejudice against Israel above all others......along with the unconscious use of age old anti semitic tropes in demonstrating that disapproval and hatred.
If a Jewish person is supportive of or attached to Israel they are fair game......and that happened a lot on Corbyn's watch. My Labour MP was terribly bullied and intimdated by her Corbynite CLP - purely because she was a 'friend of Israel'. I heard people say the most terirble things about her...as if she wasn't even fully human. Corbyn allowed that to happen, and even encouraged it. ideology come before everything else.
She was bullied out after 20 years as a good, solid constitunecy MP - and replaced with a Corbynite who now re-tweets Mermaids, and who comes out with " Israel is a fascist state",even as her constituency office is right opposite a synagogue.