If your PC is a 32-bit UEFI-based (yes, with a 64 bit CPU... thanks Intel !) PC, you'll need to install the grub-efi-ia32 package while using the liveCD before you install Devuan.
This happens when you have an Atom, Celeron Silver or Pentium Silver CPU based cheap PC released from 2011 up to around 2017.
Watch for the "IMPORTANT NOTES" section: https://files.devuan.org/devuan_beowulf/desktop-live/README.desktop-live.txt
Pretty weird from Devuan that they didn't integrate that package too on the iso. Anyway, enjoy your far less bug riddledbuggy Debian from "wontfix"-ed systemd bugs !
One other unlikely issue would be that you have installed Devuan with a separate /boot/boot, and that Devuan got a bug and wouldn't boot if you did so. This bug was in Devuan 3.0 isos, they spot it after the release and should now be fixed by now on 3.1 isos (which you do use) as it was planned.