On Wed, 19 Feb 2020, Ludovic Courtès wrote:

> The kernel’s lazy module loading mechanism invokes this program, which
> should just work.
>
> Does /run/current-system/profile/bin/modprobe exist?

Yes, it is a symlink to 
/gnu/store/d064bv2b1hrb07j2zj78i608db7qldx9-kmod-26/bin/modprobe

> Any hints in “dmesg” or /var/log/messages?

Not that jump out at me. I do see

udevd[197]: no sender credentials received, message ignored

printed in red, but that message also appears when everything is working 
correctly.

The full dmesg output is attached. The bit at the end about e1000e was 
after I manually ran `modprobe e1000e`.

Best,
Jack