I can confirm the same behavior when LVM is checked. At the end of the installation there is a popup
IMPORTANT: There may have been a problem with the bootloader installation which could prevent your system from booting properly. Before rebooting, you may want to verify whether or not the bootloader is installed and configured.
and bla bla info about GRUB Arch Wiki.
After reboot fresh lands in GRUB.
ISO 19.1, downloaded today.