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Fedwin - I suspect the problem lies with the content of the ToC in the Epub - in that the links in the are improperly formulated. I suggest you look at a 'good' and a 'bad' epub in the editor to see the difference.
You may be able to 'fix' the non working TOC's with the Edit TOC tool, if not then you should be able to fix it in the editor. In both cases make sure you have copies of the files as they are now...
You could to complain to store where you bought the book - they might even give you your money back
BR