Especially if they're carnivorous, you need enough undisturbed space to explain not just the existence of the cryptid, but their whole cascade in the food web. And probably in the fossil record too.
It's possible to imagine one individual creature existing, but it would have to be part of a population, and that population would have a restricted range and carrying capacity. Take the okapi for instance, it's about human-sized, herbivorous, and rather shy, and doesn't live outside one region. Humans still were very aware of it since the classical period, even if it took Europeans until the late 19th century to document one.
Especially if they're carnivorous, you need enough undisturbed space to explain not just the existence of the cryptid, but their whole cascade in the food web. And probably in the fossil record too.
It's possible to imagine one individual creature existing, but it would have to be part of a population, and that population would have a restricted range and carrying capacity. Take the okapi for instance, it's about human-sized, herbivorous, and rather shy, and doesn't live outside one region. Humans still were very aware of it since the classical period, even if it took Europeans until the late 19th century to document one.