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: