Why does Yanagi Polarity Disorder after 2nd shock double in DMG? (Mono shock team)

I played her in a mono Shock team with Seth and Caesar and consistently noticed that her Polarity Disorder damage always doubles after the second Shock application. I use her with her Signature weapon, and her stats are as follows:

https://preview.redd.it/9adr2b34u63e1.jpg?width=2560&format=pjpg&auto=webp&s=42298655e259175d7f366cebff0580789212e528

I applied Shock to the enemy, ensured I had the full Signature buff before launching her EX Special, and got the following damage:

https://preview.redd.it/lbkr6lo4u63e1.jpg?width=2560&format=pjpg&auto=webp&s=18d1c1abfc117083d0aa5894fc3faffa9b36518e

This is her damage after 2nd shock application:

https://preview.redd.it/a6al9sg5u63e1.jpg?width=2560&format=pjpg&auto=webp&s=de8c045583f5e815742f77285e012d6d9c54c8a3

Anyone knows why?