The bypass filter, by definition, is a tightly wrapped medium that severely restricts the flow of oil. Therefore, there must be a pressure drop across the filter. My guess is that there will be a very severe pressure drop across the filter. If the filter restricts the flow of oil to any great degree (which it is designed to do), then the pressure on the upstream side will be the normal high pressure in the system (3.0 bar at 1500 rpm and above).

Downstream of the filter, the pressure will drop to something less than .5 bar (I'm guessing here). It might drop to less than .1 bar, if the filter is restrictive enough.

The only possible way that the pressure is the same both upstream and downstream is that the filter has no restriction whatsoever and, therefore, the pressure downstream of the restricting orifice is very low. I don't believe that this is happening.