I'm starting to have the same problem, where about a third of the Sims I upload to the gallery are being flagged as modded, but they haven't been (in most cases, I actually try to limit packs, eg just 5 or 6, when dressing sims). I tried the suggestion you gave the OP, but it didn't work for me. Is there another thread I can add this glitch to? Or is there a different workaround?
@crinrict Thanks for your response! My username is gertie47 - a few examples of sims I've created that say they have CC, when I didn't use CC, are "Lyon" (ie, Kyle Lyon), "Whitaker" (ie, Asher Witaker) and "Page" (ie, Isabel Page). But there are more than that. This problem seems to have started after the last update, and I don't know if is connected to the new Grunge Revival Kit, as these sims all have items from that kit.
