Cause: You skipped a version (e.g., RX11->RX13 without RX12). Fix: You cannot fix this with a patch. You must perform a clean install of the full repack (backup UserData, delete the game, install the latest full repack).
The internet is filled with fake "UPD" files containing malware. Only use official sources. koikatsu partyrepack upd
Assuming you have the BetterRepack (the most common), here is the safe ritual for applying an "Upd". Do not skip steps. Cause: You skipped a version (e