I don't run a worm cafe but I seem to remember reading about others with this problem. A search will probably find someone who had this problem and their solution.

If I remember correctly the worm cafe is a commercial stacking trey unit? Is there any way for the worms to climb back out of the bottom try easily? I think I remember reading about an idea of putting large pieces of corrugated cardboard bedding in the bottom trey so the worms can climb back into the next trey. I think some also put in a way for the leachet liquid to drain out too.

With all that said I am going by memory of what I read not from experience. I run a traditional single level flow though and a bag type worm inn.

Plastic worm tray systems seem to be sold without instructions or at least instructions from anybody who has ever seen a worm. Worms also do not read the instructions for these systems. Then the owners who purchased these systems come to us for answers. A pox on worm tray system sellers who have never cared for a worm or understand even a single thing about them who write instructions. I hope we can help you. Some people put garden cloth in the bottom tray to keep the worms in. I do not have an opinion on that. Other people put the next bedding they are going to use into the bottom tray. This provides provides a barrier for the worms. Or it could be a home for a few. This material is then the next bedding for the top of the tray when the trays are moved around. A fresh tray of dry bedding is put as the bottom tray. This tray will absorb any drips that might find themselves in the drip tray. These drips are probably food moisture that needs to stabilize a bit before instead going oxygenless. We want all areas of the bin to be able to get oxygen. This tray then becomes the new bedding at the top of the bin. The bit of drips it catches helps to get good bacteria growing. It's a good thing.