Exact thing happened to me. Shrimp never made a reappearance. Got 2. 1 week in, 1 molted and went into hiding in a crappy spot. 2 days of hiding later, it vanished never to reappear. LFS said that they can sometimes become injured during a shed, maybe a leg gets stuck or something and they end up hobbling around looking like pray. Plus they’re super soft and delicious after a molt. I dunno. I can only assume mine was eaten. Same with yours :(
Hope your little guy’s still in there. Keep us posted.