According to this article, Toyota sets a maximum acceptable delta between highest and lowest battery block at 1.2V
I suspect this difference alone is not enought to trigger the error.
I logged two different trips on a faulty Prius 3.
The first trip didn't trigger the error.
The second one did.
In the first trip, delta was above 1.2V for 5 seconds
In the second trip, delta was above 1.2V for 14 seconds, and the error was triggered