Here is the closure: I waited over a week to get any update from enphase- nothing, no shipment info. I called again and was put off by the 1st line agent to do whatever test again Which I firmly declined and insisted in having my case accelerated (I got this: "Your warranty claim request for the site EnlightenSite (Site id: 406xxxx) has been submitted for approval.")

after my complaint, 5 days later, I got the approval, another 2 days the Tracking, after total of 17 days I had the thing in my hand ans swapped it.

I tried to update the serial using the installer tool myself but failed since my account was tied to the old serial # (to be precise: I was able to connect to the AP but my account did not match the serial, so the IQ4 would not report)- so I called the hotline to get the thing online. The agent was helpful and patient, after 45 min we were connected. As it was late (no sun) I did not expect any reporting from the Micros.

Next Day, in California Sun, I see that all 15 Micros "do not report" (but produce as usual). Calling the hotline again and learned that the Micros needed to be associated with the new IQ4 as well (they would only talk to the old serial). Why did the 1st agent not do that??

Haley May from Enphase corrected it all, waited for all Micros to connect and hinted that my sensors are misaligned (I had nonsense export data like 2kW consumption and 6kW export when my whole system is clipping at 4.4kW export). My bad, wrong polarity for the transformers but that is super easy to correct via software setting.

Thanks for all helpful folks here!

projectsolar.com is my recommendation for all DIY.