Had a similar problem to this:
I dug in the code some and it was failing on the get_posts call in the WP_Storify::upgrade() call ..
My blog has 50K+ posts and to return them all appeared to be exhausting the memory and causing it to fail.
Might make sense to store some post meta data and query based on that rather than grabbing all posts and trying to filter for the storify permlink in them.
I changed the if statement in WP_Storify::upgrade() to bypass the get_posts call.