Now I recall:
on what was written on the originally sealed package. It was year of 2018. I recall that even Anker PowerPort Atom PD 1 (probably to its built-in controller related) was not able to initiate charging of this old stock power bank. And I don’t mind on telling you which power supply did the job of waking up quite discharged power bank batteries, but this would not lead to solution on your own, not yet. Hope this description here helps anyway to understand what I suggested within my above post. With my main hope that actually Librem 5 will do the miracle with its charging chip and recover your over discharged batteries by itself (through your work around initiative).
For example/orientation article: “Just because the cell recovers voltage, do not make it advisable to discharge below the limits while current is on.”