Hi Basilis,
I don’t think that’s the case. I just uploaded new images for the last 5 reviews at a much larger size and the thumbnails are still blurry in the widget.
You’ll also notice that in my ‘top reviews’ widget in my site’s footer, the top reviewed thumbnail image has lost its proportions.
It appears those two issues occurred at the same time.
Is there anything else that could have caused that to occur?