Was it a white, almost translucent piece that you saw? Or did it have the same colour as your shrimp? If it was white, it was likely just part of a molt. Shrimp molt (shed their exoskeletons) as they grow, and right after they molt they tend to go into hiding until they redevelop their exoskeletons.
That said, aside from otocinclus, any fish can eat/target/harass shrimp to the point that they die. Some are a little less likely than others, but it can still happen. Even if you had no issues for years, it can happen overnight.
That said, aside from otocinclus, any fish can eat/target/harass shrimp to the point that they die. Some are a little less likely than others, but it can still happen. Even if you had no issues for years, it can happen overnight.