Hey there,
I apologize for the delay in my reply!
Can’t seem to find the isotope error message you mentioned above – does it appear on the front page? When you mention that “before that it was fine” – which even in particular do you have in mind?
Regarding the post content – there is a special tag in WordPress which can abstract the post at any given position; you can add this “more” link through the WYSIWYG controls in the post editor mode (in the visual mode, it’s called “Insert More Tag”, and in the HTML mode, it is the “more” button). You can read more about the “more” tag on the official WordPress website here.
Sincerely,
Andrew / Satori Studio