I've not had that problem. I tried looking into it on the Koikatsu Discord, and multiple people said they solved it by "installing some plugins" without specifying which plugins, even when asked.
I looked at the card using KK Manager and the PluginDataReader website, and I don't see any unusual plugin data listed. Do you have the latest version of the Objimport plugin installed? If not, I've attached it below. (KK for Koikatsu/Party, KKS for Sunshine)
You could also try reloading the scene/software to see if it was just a weird hiccup.
If those don't work, the only other thing I can think of is installing the latest HF Patch, in case it has the plugins you're missing.