I don't know if I'm on the right track here, but the thread has made me think about a couple of different, perhaps interlinked things.
From my own experience, I don't feel I can generalise about whether women-only spaces are automatically good and mixed spaces not good, or other way round. So much has to do with whether the people involved have shared values, agreed ways of interacting, commitment to agreed goals, willing to act in an open and transparent fashion (no hidden agendas,), there is a commitment to inclusion and where there may be differences in levels of power or influence, these are acknowledged and there is a commitment that all will seek not to perpetuate privilege.
So, on the face of it, a feminist group would seem more likely to have those "ingredients" than say a mixed gender group or a group gathered for a different purpose that say just happened to be all women. And, in my life, I have been part of some amazing, supportive, productive, creative groups of feminists where all those ingredients WERE in place.
To be fair, I've also been in a few that were ghastly - not because they were women only, not even because the focus was feminist, but because some of the people involved weren't genuinely signed up to those shared goals, values and commitment to working together. Some of the worst examples involved very painful in-fighting, often centred around a few individuals who perhaps did have their own agendas and others either felt forced to take sides or perhaps got blown out in the blast wave.
But again, to be fair, I've seen just the same thing happen with mixed gender groups (and not always polarised along gender lines,) or groups focussing on other subjects where there was a shared interest or goals. I'm thinking of a particularly bloody battle in a very small local conservation group and a couple of similar situations.
I think there may be higher than usual expectations amongst some women when getting involved in a feminist or women-only group or campaign. Perhaps the expect not only to "get the thing done" that they are gathered for, but also that their personal, social and emotional needs will be met - that they will feel nurtured. They expect the values that underpin feminism to permeate the way the group interacts and functions and how people treat each other. When that happens, it's great, don't get me wrong. But, it doesn't always happen, and I think women can feel even more let down by that than they would in a mixed group or one that's not specifically feminist. That disappointment and pain can morph into bitterness and anger, then on to arguments and personal power struggles.
I do want to emphasise that I don't think this is inherent in women's groups or something that women are more "prone" to by any stretch. I think it is something common in values based organisations, groups or campaigns - where people are involved because they feel passionate about something, and that passion may make it more difficult to hang on to "professional" boundaries, so a criticism can be perceived as a personal one when that's not meant.
That's a bit of a long prattle, but just some thoughts that came to mind.