This happens when an addon you installed overwrites the default wake (not contrail
) effect by another wake effect from FSX.
In P3D there is a change in the effect definition if I remember correctly. The coordinates of the particles (the elements that makes the effect visible) are not in the same order, like X, Z, Y instead of X, Y, Z, something like that.
Because of this, the things go vertical instead of horizontal.
You might want to find new, original fx_wake*.fx (something like that) files from P3D to replace your current ones, which are corrupted.