I have specified the following attributes in my site\'s .htaccess file:
.htaccess
AddOutputFilterByType DEFLATE image/svg+xml DeflateCompressionLevel 9 He
I suspect this is due to the plus sign in the MIME type, which may need escaping in the AddOutputFilterByType directive. You can also try using the AddOutputFilter directive instead, to process all files with a certain extension:
AddOutputFilter DEFLATE svg