RSS and Atom Feeds don't offer a content attribute. The 'content' is provided as 'summary' attribute. So change
local_entry.update_attributes(content: entry.content, author: entry.author, url: entry.url, published: entry.published)to
local_entry.update_attributes(content: entry.summary, author: entry.author, url: entry.url, published: entry.published)Nevertheless, NewsFeeds are very fickle things. So you shouldn't rely on the existence of single attributes.
Have a look at your show.html.erb
<%= @entry.content.html_safe %>You could for example use the safe navigation operator
<%= @entry&.content&.html_safe %>Or inform the user, that no content is present
<% unless @entry.content.nil? %><%= @entry.content.html_safe %><% end %>