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