Suggest editing /etc/default/grub, finding the line
And putting a # in front of it. You can optionally add a line:
Then save the file. Then run:
sudo grub2-mkconfig -o /boot/grub2/grub.cfg
Reboot and see if it's better. The above suppresses the error immediately after Welcome to GRUB but before the menu appears, and also suppresses the fancy theme which on some system is so dog slow that by the time it draws, the grub timeout has happened and boot commences.