The most challenging maps for you.

How can a stack fail to reach the nearest enemy if a Berserk unit is forced to attack the nearest one? Is it due to the force field or something else? Especially considering it's a flying stack.

Yes, there's a quirk, described in the physics engine – under the Berserk effect, the attack must be directed at the nearest enemy, but... from one side (it seems to be the right side). That is, if it's not possible to approach the nearest enemy to attack from the right (due to obstacles limiting movement), the turn will simply be skipped.