(might happen with non-svg images too - I haven't tested)
If an svg image whose default size is very small, is then embedded in an infobox and resized using |size=x property, the hovercard still shows the image in its small, default size.
Topic on Talk:Page Previews/Flow
Thank you for reporting this. Can you please provide the specific links for which you saw this, if you can remember them. Screenshots would be even better.
It used to happen in all articles linking to "League of Legends World Championship" (https://en.wikipedia.org/wiki/League_of_Legends_World_Championship), however I fixed that by editing the default size on the SVG in the infobox and reuploading it. I don't really know how can I reproduce that without screwing with actual articles... If you have a working testing environment it should be pretty easy to reproduce, just take a small svg (the one that caused me problems back then is https://upload.wikimedia.org/wikipedia/en/archive/7/7b/20141025115506!League_of_Legends_World_Championship_Logo.svg) and set it as the infobox image for an article, then link to that article from somewhere else and watch how the hovercard looks.
