@Jeremiah, Below are results from my Solar Testing that might be useful to your Application.
Device OS 2.0.0.rc-1 , Boron LTE …
Hibernate Sleep will wake the Boron LTE when the Solar Panel Cycles.
That would be similar to [you] inserting a USB cable, but you also have the VUSB pin powered, so I’m not sure. Hibernate might be worth a try.
Here’s the post.