Yep, same problem for me. The latest versions of the v12 nightly builds are the exact same.
1). Gotta flash the nightly build on a SD card
2). Insert sd card into RPI4
3). LibreELEC does a file system resize and then reboots
4). error in mount_storage. mount_common: could not mount UUID-xxxxxxxxxxxx *** error starts
5). Gotta plug off the raspberry pi and start it again, and it works!
I really think this needs to be fixed. It didn’t happen in one of the older July releases.