DId you try on an unmodded game ?
Yes, the problem still occurs. The only mods I have are gallery poses and CAS items.
I have this issue now 3 times when leaving to use my vet clinic, dog remains behind and there is always 1-7 other people home at a time so shes never alone but I always come back to her filthy. I am away between 12-20 hours. No mods.
I also have this issue. My sims leave to go to their vet clinic for the day (they tend to be gone for at least 12 hours) and when they come home all three dogs are filthy. This happens whether or not I have MC Command in the game (I've played with and without, no other mods/cc). FYI, I play on a Windows 10 laptop, I have all the packs, my game is up to date, and I regularly clear my game cache.
I also have this issue my dogs are getting dirty every single day. Without doing much at all. It's insane to have to bath them as much as a human sim (daily)
