When Squiggoth Brute uses the reaction, all enemy army units at that planet lose one instance of all keywords that they currently have at that time. This means that, if a unit has multiple copies of a keyword, such as two Armorbane keywords from Goff Big Choppa, the unit will continue to have Armorbane unless effected by a second Squiggoth Brute ability.

In the case of Area Effect, as well as other abilities with numeric values, the Squiggoth Brute clears the keyword, but not the associated numeric attribute. This means that, if a unit has two Gun Drones attached, the first copy of Area Effect (2) loses the Area Effect, but not the value of 2 associated with that Area Effect. The other Area Effect (2) from the second Gun Drones is intact. This Area Effect (2) then adds the value of (2) from the first Area Effect, giving a final Area Effect value of Area Effect (4). If the unit was then hit by a second Squiggoth Brute, it would have the (4) from the Area Effects but without the Area Effects, so would not have any remaining Area Effect keywords with which to perform an Area Effect ability.

In the case that a unit gains a keyword after the Squiggoth Brute has already triggered the ability, the keyword is not lost and functions as normal.

No part of this answer was written by an LLM, and was written by Coalback. Please contact me, or use the comment section, if you believe it is incorrect.