Raspberry Pi Won't Boot SquashFS

I can't get a SquashFS image to boot, on a Raspberry Pi 4. I have tried 21.x, 22.x and snapshot, but the behavior is always the same; the EXT4 image works, but SquashFS image does not. The device shows a frame buffer and starts doing stuff, but hits an error. The error is only shown briefly, because the device reboots after 1 second. The error says something to the effect of...

"No filesystem could mount root"
"Tried squashfs and ext4"
"Unable to mount root FS on unknown block"

I did some searching, but couldn't find anything. I tried updating the bootloader, but that made no difference. Any help would be appreciated!