Sounds like the mantis is about to molt. Mine stops eating for about a week before a molt. Then doesn’t eat for another week after. Might take some raw shrimp if it’s near it’s hole. try giving it a piece of raw fish.
If it is about to molt, don’t keep putting snails in front of it. They get soft before a molt and it can break it’s hammers off if you make them strike.
They hide before a molt because they are vulnerable, if you mess up it’s molt by bugging it, they can and will die. Best thing to do, is turn off the lights in the tank, if you can, and leave it alone.
Mantis shrimp won’t starve themself, so don’t worry about hand feeding it food, if foods in the tank, it can find it. Soft food is more enticing when they are soft, because they don’t want to strike.
They also hide a lot more aka “shy” when they are about to molt because of their vulnerability.