I would say that if fewer cases are being reported then the issue has probably been weeded out and dealt with to a large extent. There is no way the mainstream media will pass up an opportunity to attack Labour. No news is good news.
I don't think Corbyn is associated with any racist groups as such. He has shared space with pro-Palestinian groups, some of which do not come out favourably to close scrutiny. But he is a pacifist (or as close to one as a politician can be) and always promotes negotiation over force. As far as most in that region are concerned Israel and Palestine are at war and in that situation they are not going to ensure their terminology fits in with the needs of some western liberal ethics.
I think it needs to be sense checked though. Given the choice of someone who has actively supported people whose lives are blighted by living in disputed (or in some interpretations, occupied) territory and in that role associates with people who see themselves as at war and use the sensibilities or people at war. Or a government who arms and trains a Saudi regime despite their known human rights abuses and attacks on other territories. I'd chose the first guy.
Yes we expect more from our own, but if we are openly over critical of our own then we just arm those that we wouldn't touch with a barge pole. I'm all for honing and improving the Labour Party but if that in any way assists the Tories then I'd rather do that behind closed doors.
The things the Tories are getting away with while the press focus on Labour infighting is too extreme. Within a couple of weeks of Cameron quitting they had all rallied around, dropped any principles that did not fit an extreme party line and got on with dismantling everything that is good about our public services.
By continued infighting we allow that to happen.