The limited time units that were for sale during the Halloween war (October) and the current ones (November) are bugged

the problem is the smallest unit, the one with 1% bonus for 25 gems (Lich Zimxahl in October, Pilvian Apprentice in November)
in the bonuses the boost is applied but our player stats are not reflecting any increase due to Infantry Attack bonus (October) and Magic Attack bonus (November)

the other units for 75 gems, 200 gems and 300 gems at least increase our stats BUT the bonuses of none of the 4 units stacks, so buying multiple of the same unit (which is required to finish the event) does not increase our stats.

I also note that this is in contrast to the last 2 times limited time units were available in the shop, in the past the boosts on those purchased units did stack, making it worthwhile to spend gems.