There is a valve in the oil filter that will bypass the filter if there is a pressure differential of around 10PSI. When the oil is cold and thick, it won't pass easily through the filter media and the bypass opens to make sure the engine is being lubricated. When the filter is clogged, the bypass opens. This sends oil directly from the annular holes straight up the big tube in the center and into the engine. The bypass also opens when you are running higher rpm where the oil flow is highest. I know, the oil is not being filtered. But the engine is getting oil and that is the most important thing.
The oil pressure occurs as a function of resistance to the flow. If you had full oil flow going to the filter, then the filter isn't going to be where an oil pressure problem occurs. Again, it will always go into bypass is there is a flow problem. But you could have nasty stuff blocking your oil pickup and that for sure will give you some oil pressure problems. Otherwise, if all the engine parts are in tact, oil pressure lost in the engine is usually going past the cam bearings. But other things can happen, like the engine puking a lifter or popping out a gallery plug. You first need to confirm what your true oil pressure is with a mechanical gauge.
