Latest version of WP & latest version of the plugin, for me the thumbnails aren’t displayed in the media library. I made the following change to line 72:

public function styles() {
	wp_add_inline_style( 'wp-admin', "img[src$='.svg'] { width: 100%; height: auto; }" );
}

to

public function styles() {
	wp_add_inline_style( 'wp-admin', ".image-icon img[src$='.svg'] { width: 100%; height: auto; }" );
}

Which seemed to do the trick.

https://wordpress.org/plugins/scalable-vector-graphics-svg/