Hey there, I'm the one that posted the bug for invisible pets; in all of my cases I was far, 2-3 zones from home and sent the pet home via menu then tamed something I found, and ran it home. When I arrived and finished putting the new pet in a stable I'd summon my old pet to me to stable since it was left standing in the world as an inanimate object. This is where it ends up invisible when I summoned it to me back at home. I can test this on the test server and see if it's a thing there.
Test server: It appears to be fixed, and from my testing must've been related to the also-fixed full stable bug. I can however still cause the pet to stay in the world, via sending them home from a far away zone.
Pic: https://imgur.com/a/QANcWy2
Upon taming a new pet this copy disappears from the world, at least.