mjhjmtu

I tried xl console sys-net which is something that works for any other VM (AppVM, TemplateVM), it even works for sys-net-dm (I don't know what that is though)

[ctor@dom0 ~]$ time sudo xl console sys-net
xenconsole: Could not read tty from store: No such file or directory

real 0m5.036s
user 0m0.005s
sys 0m0.015s


[ctor@dom0 ~]$ rpm -qf `which xl`
xen-runtime-4.8.4-2.fc25.x86_64

For unknown reasons (bug?) you have to explicitly use the -t flag to specify the console type, which can be any of the two serial of pv. Either works!

So either of the following two work:
sudo xl console -t pv sys-net
sudo xl console -t serial sys-net

But this won't work for sys-net:
sudo xl console sys-net

$ xl console --help
Usage: xl [-v] console [options] <Domain>
-t <type> console type, pv or serial
-n <number> console number

Attach to domain's console.

[ctor@dom0 ~]$ sudo xl console -t pv sys-net 

Fedora 28 (Twenty Eight)
Kernel 4.14.67-1.pvops.qubes.x86_64 on an x86_64 (hvc0)

sys-net login:

[ctor@dom0 ~]$ sudo xl console -t serial sys-net 

Fedora 28 (Twenty Eight)
Kernel 4.14.67-1.pvops.qubes.x86_64 on an x86_64 (hvc0)

sys-net login: 

[ctor@dom0 ~]$ sudo xl console sys-net 
xenconsole: Could not read tty from store: No such file or directory

[ctor@dom0 ~]$ rpm -qf `which xl`
xen-runtime-4.8.4-2.fc25.x86_64

Note: Exit console by pressing Ctrl+]

sys-net has Virtualization mode set to HVM. All the other VMs have it set to default (PVH). That seems to be the main difference.