There are many reasons for the slippage of manual chain hoist, but most of them are due to the wear of brake pads inside the manual chain hoist. If this is the case, just change the brake pads, different manufacturers and different brands of hand chain block brake pads use for different times, the quality of chain block brand use longer.
Hand chain hoist is an upgrade of a common pulley. It uses reverse brakes and chains. After lifting an object, it will not fall (unless the chain is broken or man-made) for short-distance lifting of small equipment.