When updating a resource in the Media Library, the default behavior is to strip off any previously entered tags and metadata associated with the resource. You can keep these tags and metadata by choosing this option from the preferences page of the Media Library.
In order to do so, go to the "menu" icon on the top left of the media library. Then go to the preferences section and click to enable the option to "Keep existing metadata when uploading newer versions of an asset". Once the checkbox is enabled, click "save" on the bottom of the page.
The below video explains this in further detail: