We typically refund such bets unless they are a blatant attempt at taking advantage of the other
bettors
[...]
we did refund a very late bet even though it could in fact have been construed as a skimming attempt.
By changing this rule you are effectively telling the cheats that they will now be allowed to cheat again as long as they don't make it too obvious. You are also opening yourself up to accusations of favouritism yourself - maybe you refund some bets and not others because of who made them. We can't tell.
Using the old rule is much clearer and fairer for everyone in my opinion.