Is there a chance you folks are using a stand/docking station similar to this one?
Because I have had a similar issue, but ONLY when using the stand/docking station. When I use the same puck and cord, but no stand, I charge much faster... Wonder if even though the Ultra says is it charging the connection is not strong enough for the fastest charging?
Just a thought, but it did work for me...basically I just use the usb-c puck and charger from apple...and I have no issue, use the stand....sloooooowwww charging.