Simple search don't show up some items in 2.5.1

Hi Folks,
After a period of time, Simple Search don’t show up some items in public and admin side. If I edit and save those Items, then they are showed. I’ve reindexed many times but nothing changed.
Any idea? I’m using Omeka 2.5.1
Thanks!

Do any of the troubleshooting tips for search apply to these items (under 4 letters; appears in more than 50% of items)?

Hi, No, those tips don’t apply to these items. I see the issue is with a range of items. Por example, last items I’ve loaded are showed up OK. If I Edit and Save one of the items that are not showed, automatically they are hit.
Could it be something with MySQL updating?