With some png files, there's the uncached error which causes a 500 error:

Whoops \ Exception \ ErrorException (E_WARNING) imagecreatefromstring(): gd-png: libpng warning: iCCP: known incorrect sRGB profile

located in classes/BlurHash.php:55

    // Create a GD image from the file.
55:    $image = imagecreatefromstring($file->thumb($options)->read());
 ...

Maybe has something to do with this.

The quickest fix would be to switch Kirby's config thumb.driver from gd to ImageMagick im.