It’s possible one or more of your kitties have a bladder infection. It hurts to pee. Pee in the box=pain, therefore, box=pain. So, pee/poo elsewhere.
Bladder stones/infections can cause vomiting too.
Honestly! I hate it when people come up with completely implausible explanations for obvious paranormal events!
Ohh. Sorry. I lost my head for a moment. 
My kitty also horked this AM; however, he is trained to go to the hardwood when he has a hork coming on. I believe this is because he knows he would become a single kitty slipper if he horked on the bed.
I found three different hork piles the last two days… by stepping in it. Yuck. I really should learn to watch where I step.
Tonight my cat Spike pooped in the tub. He’s never, eer done anything like that before. He wanted to get into the bathroom, and when I tried to call him out, he wouldn’t come. He likes the bathroom and accompanying my shower. I didn’t shower for a while, then got in to smell cat shit. In the tub. Bad kitty!
StG
Almost as believable at cat pottery.
(Duct tape shut the micro-wave before they use it as a Kiln…!)
Ma-rrrooop?
ding
Hmmmmmmmmmmmm
Pah-Faffff!
Clearly your bathtub is haunted!
I’m not a cat person so I don’t have anything useful to say about that, but I just wanted to let you know that every time I pass by the thread I read the title just like the Orbit gum commercial line: “What the french, toast?”
It makes me giggle.
Very easy to cure. Years ago, this came up at a dinner party - the cat was a habitual offender with the tub and refused to use his litter box.
One of the people at the dinner offered to cure the cat - he left for the bathroom and returned saying that the problem was solved.
A half hour later, a soaking wet cat came yowling out of the bathroom. He never used the tub again.