you could always.. i dunno.. upload your save
As requested, I have attached save files of two separate instances encountering this issue. Each is labeled and ordered for clarity which I'll further detail at the bottom of this post. The files cover two fights where the bug occurred from start to finish.
Encountering the bug the 2nd time, I learned the skill Arousara which allowed me to finish off all 3 clone at once and forced the game to recognize my victory. Even if others can't replicate the bug on their end, they should at least be able to tell from my saves that I had 3 clones on screen simultaneously without the real Shizu in play.
Build: MonGirlDreams-Alpha-v24.1a-pc
Round1 A Double Doors - In the Will-Power Temple entrance
Round1 B Fight Start - The start of combat
Round1 C Real Shizu 418 Arousal - Shizu 2 (Leftmost) with high Arousal before defeated
Round1 D 3 Clones - 3 Clone Shizus on screen after the real Shizu is replaced with a clone (Victory impossible)
Round2 A Double Doors - In the Will-Power Temple entrance
Round2 B Fight Start - The start of combat
Round2 C Real Shizu 366 Arousal - Shizu 3 (Rightmost) with high Arousal before defeated
Round2 D 3 Clones - 3 Clone Shizus on screen after the real Shizu is replaced with a clone (Victory possible w/ Arousara)
Round2 E Victory - Immediately after finishing off all 3 clones with Arousara with Victory dialogue.