This is an interesting and very relevant thread in reddit. Sounds almost exactly to replicate your experience.
The golf gti engine is virtually the same.
I've also read the explanation of functions in the ea888 g3 study guide and brown and blue switches and failure is as follows.
1. reduced oil pressure (brown switch) - effect of failure oil pump goes to full power mode only. DTC Fault recorded. Oil lamp
2. oil pressure switch failure. - effect of failure - dtc fault logged - oil lamp.
Update for anyone who stumbles upon this: I put an oil pressure gauge on the car over the weekend and found that the pressures are totally within spec. Drove it around under the same conditions that usually triggers the light and found that the oil pressure was steady at 23 psi, and occasionally dipped for a split second to maybe 20 psi then back to 23 when accelerating. Hard acceleration made the system go into high pressure regulation mode, and the pressure would stick at around 50 psi until letting off the throttle. So looks like this is a switch problem. The minimum pressure you should ever see according to the service manual (for engine code CXCA) is around 17 psi, and the low pressure switch supposedly goes off around 12 psi. So the switch is probably shot.
I think both the reduced oil pressure (brown) and the oil pressure (blue) switches are bad, as in my research I found that the brown switch causes the oil pressure light to go off, and the blue switch causes the EPC light/limp mode (but not the oil pressure light) to go off. I'll replace both switches today and see what happens. My suspicion is that the switches were damaged in the past due to there being fuel in the oil, as the car had a hard start problem in the past that was introducing a small amount of fuel to the oil on crank.
UPDATE: Replacing both the oil pressure switches (blue and brown) fixed the issue! Have not had the light come back on for a few weeks now.
I'll try to post the study guid oil supply explanation sections later as well, as it is a decent read..
For the cost, if it was me still trying to get through this, I'd try relacing the full power pressure switch (blue) as well. Ruling that out. As there is interaction between the two pressure switches and the N428 oil control valve in the event of "faulty" switches.
The N428 oil control valve (on front crankcase - need to remove vbelt and probably drain oil partially at least) could be faulty as well perhaps - mentioned in previous post - if it was sticking in one mode or the other sometimes even briefly, It would mean the pump cold be in the wrong pressure mode compared to what the ECU is expecting (asking) for pressure wise.
The other thing that has caught people out with oil pressure issues on EA888 gen 3s, (but usually results in a permanent and immediate oil pressure problem) is the anti drain valve in the oil filter housing. It is a sort of stick assembly that goes down into the bottom of the oil filter housing and there were at least two different versions.
One had a spring tensioner the other just a ball joint stick pressed into the top of the oil filter case. But both feature a oring or dual oring seal at the important end to seal the drain hole. It gets pulled out when you change the oil filter (for the oil to escape). If that gets damaged, broken or the o ring gets leaky, it will leak pressure. If the stick gets broken it might not be retained to seal properly. It is pretty easy to check this when car engine cool and you won't need to drain the oil. just take the oil filter housing cover off slowly and allow the oil to drain down.
Hope this might help, but keep us updated even if it is the garage who takes it forward!
Edit: oil supply pdf self study guide attached.
EA888 OIL Supply.pdf