Yes, a softener will cause some pressure loss due to the resistance from the resin bed, but excessive pressure loss can be caused by one or a combination of the following.
1. On well water, this is usually due to fine sand coming from the well.
2. On softeners installed in the open sunlight (mostly in Florida), a layer of algae can grow and thick pieces of this growth clog the lower distributor tube screen when they start peeling off the inside of the resin tank.
3. On chlorinated water supplies, sand can get into the tank from new construction or work on water lines in the area. All of these situations are rare.
4. The most common cause of pressure loss occurs on chlorinated water. The resin can be damaged by high chlorine levels and turn to mush. This has the same effect as having fine sand at the bottom of the resin tank.