@Stjernemylder
I removed all of my mods and CC and loaded a test save in Brindleton Bay. I was not able to reproduce this problem. My household pets seemed to be acting normal & none of them were getting uncomfortable moodlets. I even added a hamster and it seemed fine too (one of the cats did become obsessed with sitting on top of the hamster house). There were too many sick or hungry strays but that has been going on in my game for ages & which is why I started using a mod in the first place. My guess is that the devs built-in pets spawning with negative buffs to create patients for the Vet clinic game-play & to me that's fine if it occurs at a Vet clinic where at least there is some chance of treating the sick animals. What bothered me was seeing all those sick strays in other areas of Brindleton Bay, like the Cavalier Cove neighborhood, where there is often nothing you can do to help the animals. Getting treatment My Sim always carries around several Wellness Treats but often I can't get the sick animal's attention to feed it the treat. Also there are so many of them my Sim would spend all day chasing around sick animals or buying wellness treats at the Vet's office!
The name of the mod I use is Little Ms Sam's "No Sick, Dirty, Sad and Hungry Cats & Dogs (NPCs)" mod. I can't post a link here but you can Google it & it should show up. It prevents stray cats and dogs from spawning with negative buffs. They can still get sick or dirty at some point after they have spawned but that's more realistic anyway. It does not affect patients at a vet clinic. It does lower the chance of a household pet spawning sick after a loading screen. It does add a new interaction called "Treat Pet" which should remove all sickness/negative buffs. This feature was added to the mod because sometimes sick pets are not fully healed after visiting a vet and no additional treatment options show up in the game. This has happened to me on several occasions & the "Treat Pet" interaction fixed it.
If you are not opposed to using mods then you might want to give this one a look. It's a very specialized mod so it won't affect any other part of your game. It mostly just runs in the background, there are no settings and the only interaction is the one I already mentioned. It rarely needs updating (the latest version from Aug 2019 is still current-- I check after each patch update). Otherwise maybe there is some kind of negative environmental effect going on with your lot? Are you playing in a neighborhood with an industrial Eco footprint?
I hope this helps :D
