I don’t use the Pro version with auto cancellation…
Could it be the difference in the “official time” recognized by GarageSale versus eBay?
For instance; GarageSale said it was OK to upload listings to eBay for next month’s allotment of 50 listings, yet it was not quite the next month according to eBay as eBay goes by Pacific time. The few test listings I uploaded were charged a fee, which eBay removed.
Would setting auto cancellation to perhaps 2 days ahead help?
Could you Mac being going to sleep and thus preventing GS from performing its tasks even though its open? I sometimes run a Automator app on one of my email accounts in a browser to perform certain repeated tasks when I take break such as forwarding email one by one as the email service does not support auto forwarding. If the computer goes to sleep it will cause this app to fail so I use the little app Caffeine to keep the computer awake for a given amount of time.