I will repeat what I added to my support case on this issue.
The behavior appears intermittent because of the way a listing is loaded on an eBay site.
If the eBay listings has not determined the capabilities of the user display, it will load the listing without any HTML iframe. So the description can see the viewers eBay site. If the viewers display capabilities can be determine (from a login session of viewing other listings), then the description is loaded into a separate frame hosted from eBay.com. No longer can the eBay site be determined in the eBay description since it is isolated from the listing.
So the Auctiva showcase uses the eBay.com to show listings instead of the actual viewers site.
So the issue will seem intermittent depending on the HTML frame for the description being loaded or not.
This design change of the eBay listing will most likely cause issue for all third party showcases and any tools that try to determine the eBay site from inside the description. I do not know how the Sellathon counter works but if it is in the description, it will show that the viewers are all from eBay.com and not other sites.
Perhaps eBay can be persuaded by third party services such as Auctiva to somehow pass a variable to the HTML frame listings with the viewers eBay site. This could be used to fix tools using the eBay site. Or simply go back to having the original site URL being used.