Sorry for the delayed response.
A broken download link would not be caused by 4.9.8 alone because WP does not have download links by default, they are an artifact of your theme or a plugin. It is possible for the 4.9.8 update to cause conflicts with certain plugins and themes. The onus to correct such conflicts lies with the theme or plugin author. I suggest you ask about this in the dedicated support forum for whatever module is generating the download links that are broken.
thank you for late answer
i already fint out the problem a removed player plugin setting cause to all media link begin to play automaticaly so installing that plugin changing the auto convert link to default solved problem