If you flash a Debian-style Linux live-boot image that’s intended for USB stick on a USB-SSD itself (for speed), it will get stuck at initramfs on boot because unlike USB sticks, USB SSD drives are not considered removable drives, yet the live-boot parameters (scripts) set to search only removable media, hence it cannot find the right device.

The solution is to remove live-media=removable as boot parameter (typically under append initrd). You can do that quickly on each boot by TAB key to modify this key-value pair out of the boot parameters and hit enter.

To make it persistent, you have to edit the scripts where these boot parameter lives. The live USB stick/CD was supposed to be mounted as a read-only volume, so we need to first remount it as writable in order to modify the scripts:

mount -o remount -w /lib/live/mount/medium

Note the -w parameter which means writable. -o means options. -o remount,rw means exercising the remount option as a writable drive (-w is alternate syntax for writable).

Make sure you have root access (to modify these files), and edit these live*.cfg files if it shows up in the following folders:

/lib/live/mount/medium/syslinux/live*.cfg
/lib/live/mount/medium/EFI/boot/live*.cfg

Then take out live-media=removable in for the boot menu item you normally use for each of these script .cfg files. Reboot after you are done.