Disabling other components / plugins did not help.
However, I used the Joomla installer to reinstall community builder and in doing so it rewrote the workflow with Membership Pro component so that the payment preceded registration instead of following it. This resolved the other issues with saving profile information as well.
We can mark this as resolved - and a recommendation to anyone using Membership Pro to install it first and CB second.
Thanks for your help Kyle!
~Margaret
