Daily conspiracy

[Angrboda]

At any depth, the sub is floating on the water below it, and sinking through the water above it.  When both sinking and floating yield equal force, it is suspended at depth.

I'm sorry Angrboda but that is not correct. A neutrally buoyant object weighs exactly the same as the water it displaces. There is no cancelling out of up and down buoyant forces - the forces do not exist.

There will almost always be some vertical movement in a horizontally-stationary sub or if dive planes are in a neutral position but that is because of upward or downward momentum and water movement.

Neutral buoyancy occurs when an object's average density is equal to the density of the fluid in which it is immersed, resulting in the buoyant force balancing the force of gravity that would otherwise cause the object to sink (if the body's density is greater than the density of the fluid in which it is immersed) or rise (if it is less). An object that has neutral buoyancy will neither sink nor rise.

Wikipedia || Neutral buoyancy

[emphasis mine]

You are simply wrong.