Very strange! Are you sure you have the correct filtering set, in the top portion of Mediabay? Are you sure you had them tagged originally on the presets themselves? Do you get listings for any guitars when you do this, but not the ones you are after?
Try and go back to the mediabay and click on the very top, left hand cornered double arrow, labelled reset filter and be sure all instrument sets is shown in the box to its right.
Try and click on the double arrow just below that, also on the left labelled clear search text. To the right of that, click the circular arrow labelled rescan disk, to be sure the database is fully updated to list all relevant results.
Try and search for the names of the presets again, or filter as mentioned to see what you come up with. The presets are surely there, it is just having you find them. They don’t disappear, or delete themselves when you change a filtering heading, they simply become ‘lost’ due to you making this change. It is not where it used to be, so you have to find out where it went and start again.
BTW, do you remember exactly which library this came from? HAlion Sonic SE Artist, Basic etc? If you know that, you can filter by library name and try and narrow down your results even more, as that is key here, get rid of all irreverent listings, so you aren’t wading through garbage and allow yourself to focus on the necessary listings.
Again, best of luck!