Pet icon gone black and other issues
I started having issues in my save when I accidentally had 18 sims and 6 pets in a household due to a wedding. I have a mod to allow for larger households but usually have it set at 23 sims and 8 pet...
Forum Discussion
If you have or can have NRaas MasterController in play, you might try doing a MC Reset on the puppy. Usually though a broken thumbnail for a sim, when the sim themselves is totally fine, fixes itself after a while or sometime soon after something about the sim's appearance changes. Are they due to age up to an adult dog soon or can you give them an accessory?
