At what current? (It would be nice if the GUI showed you this somewhere! Anyone? Purism?)
To clarify your config … the hub is connected, via USB-C, to a USB-C power source and the phone is connected to the hub via USB-C to a port that supports power delivery (power passthrough?)?
What is the USB-C power source? Did it come with the hub or are you using the Librem 5’s power adapter?
What make and model of hub?
I have a similar problem with my hub. The phone will negotiate a much lower charge current (power) with the hub than it negotiates with its power adapter. So it takes much longer to charge when docked. It does charge however. So I can live with that.