Problem with wordpress editor

I have just migrated to a new vps server. The migration was successful and website loads up fine. However, when trying to create a new post or edit old one there are a few issues I am facing.

1. The categories tab wouldn’t show already available categories. Only the ‘Add new Category’ option.

2. In the featured image tab, on selecting image from media or uploading new file, it keeps showing the loading sign forever without showing up the loaded thumbnail.

3. Authors tab is completely missing

The page I need help with: [log in to see the link]