It's to do with the case of the letters in the link. The return page is "SlopePICS.HTM". The links which don't work are pointing at "slopePICS.HTM", with a lower case s. It works on your computer because Windows is not case-sensitive for links. Your website is hosted on a server which uses Linux, which is case-sensitive. It is best to use all lower case characters on pages, folders and extensions within your website (eg "slopepics.htm"). This would prevent this problem.
What is Amazon Go and will it come to the UK? The store without checkouts or queues