The commit history is very limited (only 5 commits) which means that the commits have been large. Instead, it would be better to have numerous but smaller commits which would help in reverting changes, rebasing or cherry-picking tasks.

In addition, you did not make use of the pull requests which are a powerful tool to perform code review (even when working alone in a project).

For commercial projects, you are better off not re-inventing the wheel as you would avoid lots of stability and security concerns. Instead of using oauth2.session.dataTask in ApiAccess, I would recommend to follow the guide in the wiki of p2.oauth2

UIKit has a built-in pager view controller (just like in Android) which is UIPageViewController. This controller also have built-in support for a paging indicator. So why having it built with a custom UIScrollView and VerticalPageControl?

Across the whole project, it's often hard to follow the code as variables, method and class names are not very clear:

Subview of what? As this is the actual view containing the whole survey list, the name is sub-par.

Never use abbreviated names for variables name, be clear.

I am not following the naming of CoreApiAccess as the child class of ApiAccess. Core or Base seems to be the parent class.

Across the whole project, it's often hard to follow the code as there are inconsistent line breaks, spacing and code organization:

The platform setting is always added to the podfile but you need to comment it out:

# Uncomment the next line to define a global platform for your project
# platform :ios, '9.0'