That’s weird, the theme updates shouldn’t have anything to do with GP Premium/Blog – can you try deactivating your non-GP plugins and see if it’s one of them causing the issue?
That’s weird, because 1.2.8 had some super minor changes – mainly a new language and a couple of small fixes – nothing should have done anything to the blog add-on.
If you’d be willing to create a temporary FTP account for me and send to support@generatepress.com, I could try a tweak in one of the files which may fix it.
I was doing some tweaking to relayout the site. Also changed permalink to default and back to Month setting. And enabled masonry, seems to be working now.