LibreELEC keeps crashing immediately on boot, can't figure out what is wrong.

Create a bootable USB from another machine; either the LE installer (at the syslinux menu type 'run' and it will boot LE from USB instead of running the installer) .. or an Ubuntu LiveUSB image or similar that gives you a console or desktop to work from. You need to mount the /storage (second) partition from the internal drive and move /storage/.kodi to /storage/.kodi-old and then reboot. On boot you will end up with a clean/default Kodi config. You can then manually restore (move) files from the previous configuration over until you either end up with a working configuration again, or you discover which bit causes everything to break. NB: Safe mode is doing the same thing; moving a bad Kodi config out of the way and giving you a clean config to experiment from. If that isn't working or you end up in the same situation again, I'd suspect an underlying hardware problem, e.g. failing disk. LE is packaged with the entire OS in two files (KERNEL and SYSTEM) that uncompress on boot to create a virtual filesystem (only /storage is real). It's great for simplicity, but one bit wrong and one of the files is invalid, won't decompress, and the OS won't boot. Conventional distros that scatter 10k files over the disk are more resilient because a disk error only breaks 1:10000 files, not 1:2.