Why is it I cannot upgrade ACF Pro to 5.3.1 in WordPress 4.3.1 , I get this error:
An error occurred while updating Advanced Custom Fields Pro: Update package not available.
I am surprised!!!
Posted 4 days ago and still no reaction, not even read.
Same problem 5.3.1 to 5.3.2.1
You might want to open a support ticket http://support.advancedcustomfields.com/new-ticket/
These forums for users to help other users and unless someone has seen the same problem and figured out how to fix it, well…
Creating a ticket may get you help faster.
I should have said, the best advice that I can give is to deactivate other plugins and switch to a default 20XX theme to see if there is come kind of conflict causing the issue.