Librem 15v4 laptop now boots into initramfs/busybox, shows no errors

I’ve been running Ubuntu-Mate 20.4 for a few months now with no issues, until yesterday.
I noticed that I was at 5% power, so I plugged in the power cord, and then decided to shut down the machine, which I did via the System/Shutdown dialog.
I noticed that it took around 15 seconds or more for the laptop to finally power down, but I saw no error messages.

Now when I try to boot up, I get the GRUB menu screen, and I select Ubuntu. I then see the Ubuntu-MATE prompt for the encrypted disk password. After I enter that I get the BusyBox/initramfs prompt, but with no error messages.
I ran dmesg from there, but the output shows all at once, even with the more command. Also, I can’t select level for dmesg , the only available flag is c .
The only fsck output I got was for sda5, which showed “clean”. The others return nothing, or “no such file or directory”.
I can browse directories, such as usr, bin, etc. so I don’t think that the disk is bad.

I am running a memtest86+ now, but it shows no screen information or status at all. However, I do hear the fan, so I know that some process is running.

I checked the firmware, and it is at 4.11 (November 2019), which is a little behind the current 4.12.

Any ideas would be greatly appreciated.

Easiest thing would be to get whatever you want to keep off the hard drive using a live USB and then reinstall. I know that’s not a “fix,” but a proper fix will be harder to come by.