I always wait until the artifact bar is full before receiving shipment. It takes about a day to fill my artifact bar. To save time I check the box so I receive them all at once. And I almost always receive between 125-150 artifacts in my shipments. Except today. I only received 65 artifacts in the shipment.

Now, I did expand my cargo space, so is this just bad luck that I had today, or did expanding my cargo space have anything to do with receiving fewer artifacts? I would think that expanding cargo space would increase, not decrease the number of artifacts received in a shipment.

Well thats what happens when u get few Mass storage pods at once

Just chance. The two have 0 correlation unless you get full part way.
Also, you are better off pulling anytime you have 4k or more points.
Means more prisoners and less msps.