This is a bug we introduced in this release. We will have it fix ASAP.
There are two workarounds that you could try. 1. if your system could print to pdf, you could print each response as pdf instead of export as pdf.
2. you could duplicate the form with responses, open the dulplicate form, remove some old responses (the one that you already exported) so you don't see the 13000 visible cells dialog, then you could export each response to pdf.
Hope these workarounds could help you while we are getting the fix out.
We ended up deleting all old responses to get it working. Just hadn't had time to get back in here and post its been resolved. Thanks!