Thanks!

Did not find it in this ML but seems to be a common problem when updating, wonder what causes it:
https://github.com/yjwen/org-reveal/issues/132
https://github.com/yjwen/org-reveal/issues/135
https://github.com/yjwen/org-reveal/issues/146
https://github.com/yjwen/org-reveal/issues/148

Anyway they linked to this solution that worked:
https://emacs.stackexchange.com/questions/14763/exporting-org-file-breaks-when-upgrading-to-orgmode-8-3/16616#16616