Error Running a flow from a site (record lookup failing)

I have a flow that I have embedded on a public site in order to collect feedback from a user. The idea is the user will click a unique URL from an email that pre-populates their case ID into the flow and then allows them to submit feedback. The first step in the flow is to lookup related information from the case to identify the user before record creation.

When I access this flow through the site however, the record lookups do not work and the record creation subsequently fails.

I have adjusted all the Guest permissions for the site to give access to every object related on the flow and have no idea how to get this working.

Site: https://ultraid.secure.force.com/feedback?caseID=500d0000009Ebb0