Just an FYI, I'm all to aware of how crashing or getting disconnected by a rolling restart wreaks havoc with kitty stats. for that reason I've pretty well stopped cuddling most all of my cats, so that is definitely not a factor in my case.
Thanks KittyCats for the response.
I dont actually cuddle my cats to gain happiness anymore so this is not the issue in my case, rather it seems like its related to the sim in some way.
Im sure it will be resolved next time LL decides to do another undocumented change to the servers
KittyCatS Resident, and others, have pointed out some cases which can cause problems.
What I've noted is that, sometimes, it's just a rounding error and, if we wait 10 or 15 minutes and check back, everything will be OK. So, if you see a small difference and have not been watching the pair closely recently, it's best to remember your Hichthiker's Guide's advice .. "Don't Panic!" .. check back in a while, it's entirely possible that things will fix themselves.