Possible Frost Attribute Anomaly Disorder Value Changes
I am currently unable to 100% prove it however, I am pretty confident that the two values I referenced earlier are referring to the Disorder DMG Multiplier and Time Remaining per Second Multiplier for Frost-related Attribute Anomalies. In 1.4.1 / 1.4.2, these values were the same 450% Base + (7.5% * Time Remaining).
In 1.4.3, Miyabi's Core Stat was changed from AM to AP. Additionally, the previous two values also changed to 450% Base + (30% * Time Remaining). The fact these were changed in the same version does not seem like a coincidence to me.
In 1.4.4, this value was changed yet again to 700% Base + (50% * Time Remaining).
And finally, in 1.4.5, Miyabi's AP Core was increased from 72 AP to 90, whilst the Disorder values changed to 600% Base + (75% * Time Remaining).
As a result, this would make Miyabi's Frost Disorders noticably stronger than Ice Disorders. Currently, Ice Disorder is 525% at 10s remaining. Miyabi's Frost Disorder would be 1350% at 10s remaining, quite noticably stronger than Ice Disorder and a slight bit behind Burn Disorder at 1450%.
This also makes her synergy with Yanagi stronger as her Polarity Disorders would use this higher Multiplier.
TLDR:
Frost Disorder Multiplier appears to be different from Ice Disorder Multiplier, making Miyabi's AP Core actually make sense. However, please take this with a grain of salt until the CC servers come out and I can get actual confirmation.
If I can get actual confirmation earlier, I'll update here.