Hi, since, a few weeks ago, I’ve installed an update of plymouth, it is not showing at boot anymore. I hope this line from /etc/default/grub will help you:
GRUB_CMDLINE_LINUX_DEFAULT=“video=1366x768 resume=/dev/disk/by-id/ata-WDC_WD3200BEVT-22ZCT0_WD-WX80EC9VJ346-part3 splash=silent quiet showopts”