When the battery level drops below ~20% on a MacBook Pro or MacBook Air, macOS will decrease 10/25G Ethernet transmit performance in order to conserve battery life for the laptop.
On the Lenovo Thinkpad P15 (and possibly other Thinkpads), you must set 'DMA Kernel Protection' in the BIOS/UEFI to 'Disable' to allow the Solo10G to function in Windows.