When logged in and going to item comments, select ‘Buyers & Author Only’ from the drop down, page goes blank. Result:
Request Method: POST Status Code: 422 Unprocessable Entity
Also when posting a comment on your own item page, the page that appears aftwards is also blank. The page that appears afterwards has
?filter=All%20Discussion in the URL which seems to be causing the issue. ( example )
I noticed this when clicking on some google results and getting a blank page. Luckily you only get a blank page when logged in, so it shouldn’t really affect new buyers.