I can't download reports as it tells me I have no defects over the evaluation period, which is untrue.

There is another way to work out who left the low DSR's, but it's slow and time consuming, but if it's the only way for you, then it's worth it.

In the seller dashboard, on the left, click on Detailed Seller Rating Reports, then click create report. Where it says 'report type', change the drop down to item number. 

Next, find 10 feedback where you KNOW you got a 5 star rating from each buyer. Take the item number from those listings and put all 10 of those numbers in the box, separated by a comma. Give it a name (I just use a number, e.g 1) and click 'run report'.

After a minute or so, refresh that screen and keep refreshing until it says the report is complete. Open it up to check you did actually get 5 stars for each of those transactions. If you did, close down that report window and next to where the report just downloaded, click take action, then run similar.

Remove the last number in that box and then add the item number of the transaction you think may have given you a low star rating. Keep doing that with all the item numbers until you find it.

Item numbers can be found under each feedback if you don't make your listings private, or they can be found part way down the screen on the right above your description, if you click on the actual item...which you can find under the deleted items on your sellers page.