We are still running Acrobat X Pro on Windows. We have a recurring issue with documents containing transparency in combination with any spot colour. The document shows up correctly in freshly restarted Acrobat (pls see attached "acrobat-0"). However, when re-opened without previously closing and re-starting Acrobat (i.e., just the document had been closed, but not the application), the document doesn't show up - although it is open and can be worked with to some extent (attached "acrobat-1,2"). Once Acrobat is re-started, the document displays correctly again.
This does not happen if the same PDF has been created as flat (PDF 1.3).