Buyers pulled out over lack of comfort with the share of freehold arrangement?

I'm so confused, we're almost at the point of exchange with these buyers who have gone through multiple surveys, enquiries, etc and have their own sale lined up, and they abruptly pulled out this week over 'discomfort with the arrangements over the share of freehold'.

It's a London flat, in which the 3 owners of units in the building collectively own the freehold (there were 4 flats, two of which consolidated. Shares are 25%, 25% and 50% respectively). We contribute to a reserve fund each year proportionally, and the amount is determined by the amount currently reserved, regular expenses (insurance, audits, etc) and expected repairs/upkeep to the building. It's usually 600-700 a year.

I would have thought this was a selling point of the flat. They've asked loads of questions about it (and it's probably not helped by trying to explain written responses in the forms through two sets of solicitors). But now they've pulled out?

I'm scratching my head - do you see what the issue might be?