Good Morning Samuel, 

Thank you for contacting the U of M Extension Service. 

My first thought is that it is slugs that are active at dark. There is a way to set a trap for slugs to see if this is the problem: https://extension.umn.edu/yard-and-garden-insects/slugs#handpick-or-trap-slugs-298062  

The above information discusses traps and bait for the slugs. With all the rain and wet weather we've been having, it is perfect weather for slugs. Here is another link all about hostas: https://extension.umn.edu/flowers/growing-hostas-minnesota

Good Luck!

Samuel, 

Slugs are active at night. This might be why you are not seeing them. Have you tried a slug trap as listed in the information? Try that for a few nights and see what you come up with. 

Otherwise, do a careful inspection of your plants for other pests. 

Good Luck!

Samuel, 

The information states: 

Set out several flat boards, shingles or damp newspapers

• Check under these traps the next morning and kill any slugs that are hiding.
• Repeat this step every night until the slug damage is no longer present.

Set out beer traps

• Bury containers into the ground so the top of the container is level with the ground.

I have no other thoughts than the information I've already given you. 

Good Luck!

You are welcome!