Why does my cat suddenly refuse to use the catio?

What people tried

Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.

1. 1
   hiding under the bed or in an indoor cat tree house
2. 2
   inspecting the catio for structural damage or intruders
3. 3
   checking the cat's body for wounds
4. 4
   trying multiple litterboxes spread throughout the house
5. 5
   experimenting with various types of litter like clumping, non-clumping, pine shavings, sawdust, dirt, corn husk, and crystals
6. 6
   closing the cat in a small room with food, water, litterbox, and bed
7. 7
   using anti-diarrhea food additives, specialized GI prescription food, and Feliway anti-stress pheromones
8. 8
   letting the cat go outside

In their words

Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.