The text seems to imply that the +2 cognitive defense should be always active, but the character sheet is treating it as just another form one can adopt, one called “void Spren”. But if so it’s far and away the weakest of the forms, and that doesn’t seem to be the intended implementation.
We’ll take a look, thanks for the query!
Following up here! The cognitive defense increase is always been added when you have Ambitious Mind. You can click on your Cognitive Defense to see the additions there, which you’ll see a +2 from Ambitious Mind no matter your form:
The toggle is for the additional effects of the Ambitious Mind feature that follow that line.
Hmn that still makes it strange that toggling Ambitious Mind turned off any other forms, has that functionality stopped?
That is also intended, the additional effects of Ambitious Mind are a form toggle–this doesn’t impact your +2, it’s tied to the other effects. 
“If you later gain a talent that grants you forms of power, you can then use your Change Form to attract a Voidspren. Bonding with this Voidspren follows the same rules as taking other forms.”
Right but thats describing the other forms lower on the talent tree, there’s no effects listed for “void Spren bond” other than the once per day possible stun that I thought applied to all forms of power from the next tier. Otherwise there’s really no drawback to those forms.
So when I have envoy form active, I should also have voidspren bond also active, voidspren bond isn’t a separate form. If it did (and it doesnt even apply the +2 cog def) then it gives no bonuses, making it an absurd thing to turn on.
Currently, that is how the rule is presented–it may have more information that ties into the full book once we get full information on Spren, but for the playtest content that is how it is made to function.
(FYI: We’ve sent an ask to the team at Brotherwise to get clarification!)