It would possibly help if you said what the items were, as without knowing any answers can only be guesswork as you have all the information.
I would guess that the buyers premium may be involved, as if you have set minimum offers accepted, an offer from a buyer for say £50 includes the buyers premium, so the real offer, the amount you would receive would be something like £47.40, which could be less than your minimum, do gets rejected
Please note the £47.40 is just my estimate having worked out buyer premium in my head.