I've had the same issue today. I posted about it on the Eco Footprint Bug thread as it happened while I was testing that. For me it seems to be triggered by using the vet station to examine a sick pet. I have now twice had all 5 cats instantly disappear from the lot after I have tried to examine a sick cat. This is what I originally wrote on that thread.
"I was happily playing with my hermit sim, when all her cats disappeared. In an instant! Ivy had just woken up and was pottering about. I noticed one of her cats was sick, so I clicked on him and selected 'start examining' as Ivy is a vet. Nothing happened. So I tried again, and then all the cats vanished! Their icons were greyed out as if they'd run away or were out exploring. Calling them had no effect, clicking on their food bowls to call them to eat didn't have that option. Having just spent a long time making the other lots on her island as environmentally friendly as possible and having not saved them (whoops!), I didn't really want to quit without saving. So I had all of them visit another lot together. This brought back all the cats".
"It's happened again! Trying to examine a pet on the vet station resulted in all of them disappearing. Oddly I was able to examine and treat the original sick cat before, althought not without problems. The first examination resulted in the cat jumping off the table and going up 2 floors to play with another, but the action wasn't cancelled on my sim's list. Cancelling it and trying again worked."
Oddly enough each treatment, or attempt at treatment, required 2 tries. The first would not work but the pets would remain. The on the second attempt all the cats disappeared on 2 occasions, but on the 3rd occasion I was successful in treating the cat. I've invited the cats over again and have treated the sick cat. However the stars flying round his head remain! This is what I get for breaking my policy of never buying an expansion while it's brand new!
This is on a brand new Median Erazer laptop. I have a large collection of CC which includes: unlocked buydebug items, several of Bakie's animated wildlife mods, Kawaistacie's farming mod, assorted walls and floors, custom plants, custom paintings and a fix for pets spamming sims with attention.
I have the following packs: Get Together, Cats and Dogs, Seasons, Island Living, Eco Lifestyle, Outdoor Retreat, Dine Out, Parenthood, Jungle Adventure, Realm of Magic, Cool Kitchen, Movie Hangout, Backyard, Vintage Glamour, Toddler, Laundry Day, My First Pet, Moschino, Tiny Living.
