Sent refund. The big was valid but came in as a dust vote.

The window was so busy and our vote weight is so high ($500 now), that the smaller 1 SBD bids were too small to be an "effective vote" and it got rejected. We haven't had this issue in a long time and the only solution would be to raise our minimum bid again. Luckily, that amount of bidding at once almost never happens. I made an adjustment to our threshold so it hopefully won't happen again.

Since this was not a user error, I am able to provide a refund.