Wrong data on page

One of our clients uses your plug-in as an automatic enquiry-system.
Clients fill in some data, calculations are made and the result is mailed to the customer and client. The form redirects and some of the data is also shown on that page.

The email output seems te be working fine; but the data on page is broken. It shows data from a previous entry; or just spoof data. Not the data I filled in anyway.

Any suggestion what might be causing this? Or better yet, how to fix it?

//Link is to live site, but contained page.

Kind regards,
Remco Jansen

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