The regulated pressure is what it's at when the pump stops. I can almost guarantee the problem is not with the filter/regulator unless maybe it's not the right one or plumbed in wrong. I find the 80 PSI (at the rail right?) really hard to believe especially without setting a code. We had someone saying a while back they had 80 PSI but turned out to be a mistake, otherwise I think unheard of.

Fuel pressure plumbed back to the vacuum/vent fitting at the regulator might create that scenario but someone would have to really go out of their way to make that happen.

Someone installing the rollover valve (jet pump side) incorrectly or something messed up with the relief valve (on end of third hose going into the pump well) or line going to it, might cause that problem and also still let the jet pump operate.

Again assuming that the engine running pressure really is 80 PSI with out setting a code or even showing up big time on your fuel trims.

You never answered if you are using a BMW specific diagnostic platform that can get all the codes.

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1988 325is (purchased new) sold
2004 X5 3.0 2005 X3 2.5
2008 X5 3.0 (new to me)