Hardware related service qubes require static amount of assigned memory at boot. Those being greyed out is because you cannot assign different minimal and maximum memory values. There is no memory ballooning on HVM virtual machines, which is what Qubes depends on yo provide PCI device passthrough, required for sys-net and sys-usb.
Other “PVH” based qubes (normal qubes) provide memory ballooning so that memory can be “stolen” from a qube where available and given to another where needed.
The easy way would be to start a terminal over sys-net, and then ‘sudo journalctl -f’ to track logs as they are produced until your behavior shows a corresponding kernel error message on screen.
Otherwise, logs need to be searched for. A good starting point is to search for errors, with something like ‘sudo journalctl --boot 0 | grep -i error’ to search logs from current sys-net boot session for error, non case sensitive.
You will have to fix your vm-pool error first, pointed in other issue first, of course.