I think this might be a similar problem for Labour as anti-semitism in that they don't seem to grasp the political ramifications. It's not so much whether it really was an issue in the Labour Party, rather it was perceived as such and they underestimated the ongoing fear in some Jews that it's always lurking around the corner, that you have to keep your suitcase packed at all times, that it's never quite gone away.
Likewise it is easy to underestimate the concern many women have on this issue, that sense - I'm a bloke so call me out if I'm wrong - that they've only got so much, there's two successive blokes in the White House in their 70s when no woman twice as qualified would get on the ballot, a scruffy clown in no 10 until recently and a whole load of other things to contend with and now we have a political party not quite even able to say, okay, this is what a woman actually is. It's like, men have got everything and making a hash of it, now they want to appropriate our gender and take it away from us too.