Changes made to Special:Search for T306883 break Special:Search on Commons.
When searching for files via Special:Search, cropped, squared thumbnails are shown instead of the full, uncropped ones. That may make sense when searching for articles on Wikipedia, but it does not make any sense when searching for images. There are still many users who prefer Special:Search instead of Special:MediaSearch on Commons for various reasons and this breaks their workflow.
Possible solution: In a discussion at the Commons Village pump, it was indicated that this "this could be fixed with a wiki-specific CSS override, in order to restore the traditional way of rendering the full image within the available bounding box." Please do that.
Relevant discussion: Did the Special:Search display change and break?.