sjpoolowner,
It's unlikely that the line is plugged bcause most return water is filtered prior to returning to the pool. Sometimes a dirty filter will magnify a situation where return lines are not well balanced.
You can try cleaning the filter. And you can also flush the weak return with a garden hose in case some constuction debrey might have been trapped.

What happens when you take your hand and cover the working one?

I agree with the possibility of a dirty filter. Our pool has a DE filter and two returns. The return closer to the filter has considerably more pressure than the one at the other end, so we use an eyeball fitting on the closer return, and it helps to balance the pressure.

When the filter needs bumping (cleaning), there's almost no pressure from the further return. After bumping, both returns are fairly even again.