There is a similar thread here: https://community.ebay.com.au/t5/Technical-Issues/Feedback/m-p/2516863#M9039

And... it just happened to me too now. There are options to close the window, but they just don't work.

If you refresh the page you don't have to close the tab though. It just says they can't find the transaction to give feedback, then you can click on the eBay icon and go to the main page.