unfortunately, that's a very common problem on ebay that many dont notice (because many dont bother to try to search for their listings)
sometimes items show up in a search within seconds, sometimes minutes, sometimes hours, sometimes days. sometimes it takes a long time for ebays servers to get the new index information (which is what it uses for searches) and sometimes items just mysteriously vanish for no reason from the site (or at least from not showing up in a search), only to reappear later.
Back on dime day, I had 2 or 3 items that for at least 3 days could never be found via search. They were there, for they showed up in myebay and showed up if i pulled them up by item #, but a search wouldnt reveal them and they couldnt be found in my ebay store.
If you have an ebay store, keep an eye on your total items that it shows as available on your store's front page. that number will often change from time to time (sometimes can sit there and refresh over and over and watch items disappear and reappear)
It's been going on for a very long time, and with recent changes to search (which are supposed to continue happening over the next couple of months) will most likely not get any better anytime soon (in my opinion)
but yet ebay claims that there's nothing wrong with the search
