This happened to me with my HC. I had a great lush carpet of it, then the whole thing just detached gradually and I had to rip it out. I restarted with glosso.
I think it happens eventually, but some plants do it more easily than others. I am hoping my glosso will last longer than the HC, for example.
FWIW, my LFS guy suggested I vacuum up the top inch or two of substrate, then lay down another inch of new substrate, before replanting the glosso. That's what I did, and it wasn't actually as difficult as it sounded. Not sure how much of a difference it made, but he said that, with Aquasoil at least, it tends to give up its nutrients over time, and the second carpet will never grow as well as the first.
Bump: And, obviously, close trimming should help delay if not prevent the phenomenon.