It would pertain to all cell types. To be more clear perhaps, two (same) cells whether connected in a series or parallel would have the same watt hours when paired. https://milliamps-watts.appspot.com/
Escribe will show what the voltage of the cells are under load. It sounds as if the board is not getting good power. Might be the batteries, might be bad connection(ect.) of battery contacts to battery. Might be bad solder joint somewhere between batteries and board.
Where you bought it if new, Lost Vape service center or a ticket with Evolv. 4.2 volts is full charge for most Li-on cells, there are some that are 4.35 volts.
The curve can probably be found on this forum. I calculate 12.5% less than stated mah for 18650's ( on a 200 board) Keep in mind that only the "fuel gauge" is effected not battery performance with the csv
If it's the same hardware cutoff as the 200 it won't make much difference if set below 28.5 volts. I don't know what the hardware cutoff for the 250 is though.
You need to RMA the board, it appears there is a problem with the battery management section of the board. https://helpdesk.evolvapor.com/index.php?a=add&category=1
I would think that you will be asked to send them your bad board and they send you a new one.....that's usually what happens. They're pretty good that way.