I have a few comments about this situation.
I trust
@Mountaingurl in her observations of what happened. The car ran poorly with a particular oil filter compared to before and then ran back to normal when changing back to the usual oil filter.
What I'm not sure of is whether or not the anti-drainback valve was the culprit, or the bypass pressure, but neither of those
should have caused that kind of issue.
Unless Subaru uses a reverse flow method for certain engines, the anti-drainback valve should not produce any resistance to flow. It's a one way valve and normally like
@plain OM says, all it does is prevent leaking back out the part of the filter that oil normally enters the filter.
If the bypass pressure is too low, then the oil will partially bypass the filter media if the filter media is restrictive, but this too should not impede flow. It's function is to prevent flow from being impeded by clogged filtering media.
But for whatever reason, whether it was a single defective filter somehow, or if the root cause is the bypass pressure, or the anti-drainback valve, or just coincidence, it just makes sense to stick with what works. I'm presuming the oil used hasn't changed, like using additives or changing viscosity or some other variable.
