I have done an 3.12.1 install on a physical hardware in the same way as 
described.

But other arch Linux EEE701 5.4.72-0-lts #1-Alpine SMP Mon, 19 Oct 2020 
06:22:29 UTC i686 Linux

sudo lxc-create -t /usr/share/lxc/templates/lxc-download -n CONTVM1 -- 
-d alpine -r 3.12 -a i386

and sudo lxc-start -n CONTVM1


EEE701:~$ sudo lxc-info -n CONTVM1
Name:           CONTVM1
State:          RUNNING
PID:            2776
CPU use:        0.85 seconds
BlkIO use:      4.00 KiB


Eventually some CPU related stuff?
Affinity, NUMA, ???


I am looking for an amd64 phy HW to test further.