Amanos are great escape artists. I've found them crawling through my house of a morning some 10 or so meters from the tank and still going strong. So I'm guessing if there is something they're not happy with in your tank they'll make a break for it in the hope of finding pastures new.
It's something that happens in my injected tank and hardly ever in my low-energy, which leads me to conclude it's a CO2 related issue. I've turned my CO2 down and so far absconders are fewer...
However, my cat is also partial to shrimp breakfast so I wouldn't be surprised if the furry little bar-steward went fishing for them as well...