Doing some debugging of the pd communication and reading the fusb302b datasheet I think the problem is now known - the fusb302b chip is not detecting the connection of a charger when the pocket is turned on because the USB VBUS on the pocket side is powered by default.
Why this blocks some chargers and not others is not clear to me - maybe the charger and pocket are then fighting over the voltage of the line, or some chargers automatically send a packet on cable connect. /shrug The fusb302b depends on a change in the vbus state (among other signals) to trigger PD communication with the charger.
The end result is if you disable the Pocket’s charging port VBUS power in firmware it will charge while the pocket is powered on. At the expense of it no longer being a host port that can power devices. (I tested this and my anker and other brand chargers now charge the pocket while powered on)
The datasheet for the fusb302b documents the behavior for detecting and switching between source/sink mode. The Pocket LPC firmware does not implement this currently, but hopefully someone will implement that (I will try if I have some time).