Re: Sims 4 Wellness treats don't work

I test it in my vanilla game (created with Patch 1.82.99.1030) which have a lot of sick strays (I hate this feature too). I test it with strays without household, in my household and as last with treats which make you pet sick. I could all my subjects cure with wellness-treats without issue and all visual effects got immediately away.

So, I think crinrict is right and you are just unlucky and get this one bug. If you get another sick stray, please add it to your household and test if vets would work. If your pet still suffers from effects, please make your pet again sick with a treat (stinkinator, swampwater, nutrition bar, cinnamon etc.) and try again wellness treat or go to a vet.