I am sorry that I am not sure if I understand your issue here.

Do you mean that imported feeds don't auto-update from your site if the author updated the blog content from their article page?

Thanks for your answer,

I mean ... on the external site are articles, I import them daily. Sometimes, on the external site, there are new articles, these articles are imported ok.
But the old articles on external site are updated very often. And if I do the import, these articles remain unchanged on my site. How to also update these older articles?

Oh, actually it is the correct behavior, if the article is already imported on your site, the system will not update again even the original article content edited.

Because the system will log the imported article into this table #__easyblog_feeds_history from the database so that feed importer will never import/update again for these articles if those articles have already been imported in previously.

Unfortunately, it is not possible to update those older articles unless remove the imported article then import again.

And is there no way how to change this? Even if I have to change some files? Could you point me to the right direction?

Ideal behavior for me would be, to update all articles every time the import is executed.

This is very tricky even you want to modify the code because you need to modify the whole feed import workflow already.

Default workflow:
1. The system will read the RSS feed file and import the article content in Easyblog.
2. Once the article is imported in Easyblog, the system will record this article as imported from the RSS feed.
3. So it will not import this article again when the system runs this feed importer again.

For example, this modifies workflow version:
1. After the above 3 steps, the checking part need to change e.g.
- Ensure that RSS feed always show all the article post because some of the RSS feed might only show the latest 20 articles or maybe less than 50 articles.
- probably need to check whether this article was imported before or not, if yes, need to do the comparison of whether the current article content has been updated or not.
- If the original article content is updated, then need to update the content in the Easyblog post.
- This might affect the performance issue as well since need to recheck the existing blog post whether needs to update or not.

If you want to try to modify this, these are the files that handle this import feed process.

JoomlaFolder/administrator/components/com_easyblog/includes/feeds/feeds.php (import function)
JoomlaFolder/administrator/components/com_easyblog/models/feeds.php (isFeedItemImported function, this is the function check for the article whether import it yet)