[UPDATE - 20th November 2013)
An update has now been released to address these issues:
3.1.1 will now be the default installed package when upgrading.
If you already updated to 3.1, you can easily update to 3.1.1 using the following guide:
We have seen a couple of reports of issues with billing plans following the 3.1 upgrade, our team are working on providing a fix for this and will be running through QA testing over the weekend. We hope to have this through QA and available early next week at which point we will update this post.
If you do use the OnApp billing plan functionality we would at this stage suggest to hold off from updating to 3.1 over the weekend until this is available. If you have already upgraded we will make an additional update available soon to resolve these issues.