It’s not just you, it happened to me as well on my secondary laptop with an AMD APU using GNOME Wayland. I held off updating plymouth for awhile as I couldn’t figure out why it was happening. No one has posted any complaints for the gdm-plymouth & plymouth AUR packages, so I figured I’d push the plymouth update while I was updating gdm-plymouth.
Whatever is causing it, I’d prefer not to keep downgraded packages. Let’s see if it affects anyone else and and figure out what’s causing it.
EDIT: Just to be sure, make sure you’re using gdm.service, not gdm-plymouth.service:
systemctl disable --now gdm-plymouth
systemctl enable --now gdm
This can be done from a TTY if necessary.