@picsil Yes but seems to be a Particle code issue. I just flashed a version not calling any PMIC calls and it still died on startup after 1-sec white LED when powered from USB only. Then I installed V1.4.0 (see above) and it worked.
In other words, the same code that worked before without any issues repeatedly caused the Boron to crash.
I am doing more tests and noticing many similarities to this thread: 1.3.1-rc.1+ change to Boron solar charging (via VUSB) behavior