I believe I discovered a way to prevent the practically permanent non-mirror Jessica transformation. Until the cause is understood and solved, I noticed that when I obtained Jessica transformation, if I approach Jessica's bedroom door but did not actually enter, I could continue with other actions and the transformations would ends pretty consistently around 7200 frames like you said. Only 4 tests have been done by me, but hopefully this helps the others get past that nuisance for the time being.