Particle Boron not Powering Up

I have a PR54-3 that holds a Particle Boron. I am having a hard time getting the Boron to power up with just the PR54-3 supplying it with power. I need to “jump start” the Boron, either with USB or LiPo battery source. I need to power up the Boron, get it’s status LED blinking, then power up the PR54-3. Then I can remove external power source to Boron and it stays running. Simply powering the PR54-3, which in turn powers the Boron results in the Boron not (fully?) booting up.
I believe the problem may lie in the fact that the PR54-3 provides 3.3V (actually ~3.9V without Boron present) to the 3.3V pin. When Boron installed, this is reads to 3.3V. The Boron’s Datasheet describes this pin as:
This pin is the output of the on board 3.3V step-down switching regulator (Torex XC9258A). The regulator is rated at 1000mA max. When using this pin to power other devices or peripherals remember to budget in the current requirement of the Boron first. Unlike the Xenon or the Argon, this pin *CANNOT* be used to power the Boron.
Am I on the right track? Is there a way to disable this pin on the PR54-3 from being powered by it’s power supplies?

The LTE ic on this board takes a lot of power and will need an external kick during initial boot. we recommend using the battery all the time.