I've the same problem: The 'Place order' button does not show up, when PayPal Plus is selected as payment methode.
I changed the theme to the default theme and it finally seems to work (!), but with my customized theme it doesn't.
Thought there is an easy solution:
Changed the layout and template files, of the checkout and review, with the default files from 'magento/app/design/frontend/base/default'. There is a 'strange' thing happening, I suddenly couldn't manage to get past the first step (billing informations).
How to make the default checkout work on my customized theme?
How to solve this bug? What I made wrong? Anyone had the same problems?