hello @wpomeroy ,
turn on the _debug mode and see the web app context.
in general if you create the "Page (v5 compatibility)" with questions the xpath to that field should be:
ctx.webAppLogRcpData.your_input_name;
Also you have to make sure the survey option is checked in advanced properties of the web app:

if your form is ready with variable you want to save add Script activity and add in it logError() to stop processing and to show your web app context variables it will look similar to this:
<ctx lang="en" score="0" date="2020-05-06T07:50:23Z" _target="web" webApp-id="88878798798798" origin="neolane" _folderModel="nmsRecipient">
...
...
<vars>
<my_context_var>your context variable</my_context_var>
</vars>
<webAppLogRcpData>
<your_input_name>
value
</your_input_name>
</webAppLogRcpData>
</ctx>
Marcel