Huge Decrease on my On-Time Delivery rating over 1 late delivery

[kuroshiyuzuha]

I've got my first client this first week of February, since then I delivered all of my orders on time and manage to maintain my 100% on-time delivery

I got my 1st late delivery and the next evaluation my delivery rating decreased to 90% and then suddenly lowered to 89 and then now it's 88??????????? it decrease again even though the next evaluation is next month

I only experienced ONE LATE DELIVERY  out of my 25 orders since February and I don't know what to do, I can't just leave it there slowly decreasing.

(i also got small info that happens to me sometimes, it is where I deliver it on time but the client isn't claiming the order yet. I don't know if that also affects the ratings but just in case I'll leave it here)

[jonbaas]

Your on-time delivery rating only includes deliveries from during the past 60 days. The fewer the deliveries you've had during the last 60 days, the larger your decreased on-time delivery rating will be. 

[theratypist]

How many orders have you completed within the past 60 days? Compute this one order against the total orders you've done within the past 60 days and you'll have the rate you have now.