High pool filter pressure is typically caused by a large volume of particles being filtered from the pool water. When the pressure in the filter increases, it is time to backwash it if you are using a sand or diatomaceous earth (DE) filter.  Torn grids definitely need to be replaced. If the grids are torn the DE may be going into the pool itself and clogging the filter causing the pressure to go up. Fix the grids and you’ll likely fix your problem. Good video on the subject if you’d like to learn more.

From what you said the DE isn’t coming in through the returns. Most DE filters incorporate a PVC standpipe that links the manifold, and a tiny o-ring on top of the standpipe that seals the manifold to the standpipe. If this o-ring becomes lost or cracks, minor amounts of DE and dirt can be returned to the pool. Pressure problems can also result from a faulty gasket or o ring. If you see DE coming out through the skimmers, the filter is backdraining through the pump. If that happens, you’ll need to find the air leak in the pump. If you’ve check all that check your pressure guage isn’t malfunctioning.

The air bleeder (sometimes automated, sometimes manual) located on top of the filter tank is used to vent air from the tank during startup. Open it before re-starting the filter pump. If it spills water, the air relief stem’s o-ring is likely missing.