Quite a few times now I have used facial recognition, maybe set up with only 3 or 4 faces, and found that one after adding hundreds of photos, one person of the named people has disappeared. Now it's probably something I have done but my point is that this doesn't seem to be rock solid.
With most software whether its MS Word or even Premiere Pro It's not possible for something to just magically disappear!
Once you have created that named person at the top, NOTHING should delete or rename that person without Lightroom explicitly asking if you want to delete this. Right now it seems that's not the case.
How many names missing since you created them in Lightroom? you may try resetting the Lightroom preferences back to default and check if that helps, refer: Erroneous compatibility warning with Edit In Photoshop