Perhaps OT, but it might involve DIY items.
I've just been searching within Amazon for several items. When I decided which ones I wanted I opened them in each individual webpage and clicked on "Add to basket". Amazon responded with an error message to the effect that it did not recognise the webpage the order was made from. That was very odd, as the webpage came from inside an Amazon search!
On a hunch I returned to the "unrecognised" webpage, and from the URL deleted the question mark and everything which followed it. The hundreds of characters deleted are only of use to Amazon (assuming they're correct...) and are for tracking. On going to that stripped-down webpage the item I was after reappeared without all the tracking junk in the URL. I was then able to add the item to the basket without any problem.
This may be of use for anyone else having the same issue.