I have the same problem. There is an issue related to the usage avia designer. Use standard editor and the content is shown. This is in my opinion a work around and not a fix and of course really annoying.

This is still an open issues since almost a year! https://kriesi.at/support/topic/blog-page-not-showing-full-content-of-recent-posts/

Guys, when do you plan to fix this?! Quick answers highly appreciated.