@7dcjmach
Sometimes I can make it to page 2 or 3 before it happens
eBay's search URLs have some odd quirks -- one of them is that a search URL contains all the search terms and exclusions of the current search, but also may include the terms and exclusions from the previous search. In practice, this means that if you try a long URL search after a short URL search (with few terms or exclusions), the long URL search may work fine, but if you try a long URL search after another long URL search, the search may fail. Hence going from page one to page two of a long URL search is much more likely to fail.
A search for the term test may contain the following terms in the URL:
https://www.ebay.com/sch/i.html?_from=R40&_nkw=test&_sacat=0&LH_TitleDesc=0
Note the _nkw=test term which corresponds to the keyword.
If you run the exact same search again, the URL may contain the following terms
https://www.ebay.com/sch/i.html?_from=R40&_nkw=test&_sacat=0&LH_TitleDesc=0&_osacat=0&_odkw=test
The keyword and category terms are mirrored; the _osacat and _odkw refer to the previous search category and keywords, which you can see if you change the search term or category and search again.
I am not sure why eBay chose to set up their searches that way; as far as I can tell, you can delete all the terms that correspond to the previous search without affecting the results at all. The terms may have some use to eBay internally for diagnostic or statistical data gathering purposes.
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