Why are my Sims' base body templates changing?

I'm getting this with every single sim in my save file now. They'll change their body shape as soon as my sim ages up. I'm also struggling to get the cake to age up any of my sims. I've removed all my mods, cleared the cache, repaired the game, etc. The only way I have been able to fix any of these things is with mods (which can either copy the old appearance or freeze it).