Since the update, any dogs outside a container, have poofed. And also any dogs found with a dog whistle after, even if kept in an intentory or box, also eventually vanish.
Its hard to tell if anything triggers this, other than Time. The item appears in your inventory. And you see the dog model outside when dropped. But after so many minutes. Gone.
Its lots of sadness. Cause I love the doggos... And I finally managed to find catnip. But im afraid to use the items, and find a catto, only to have it also poof.