What is the shock effect value?

I have a Dawnbreaker with a Crucible tree that has shock on block. However, it says shock increases damage taken by 15%. Even though this is supposed to be 50%, there's also another node on the crucible tree saying 50%.

Is this a bug or is this a different type of shock?

I guess normally the shock effect depends on how much damage you did, but with shock on block you didn't do any damage. So it could be a different type of shock with a set effect instead of dependent on damage.

The item can be viewed in my profile in my inventory or alternate weapon.

Shock increases damage taken by up to 50%.

As you mention, shock is normally applied based on the damage of the hit. Sources of non-damaging ailments that don't hit have set values for the ailments they apply instead, such as chilled/shocked ground.

Increased effect of shock/non-damaging ailments would affect the 15% shock you'd apply on block, up to the cap of 50%.