I also see this in various version. In the end, I think this is due to the fact that somehow the file system permission got messed up. You can try the server version and you will be able to log-in. But then sudo will not work due to permission problems. I suspected that the pp "Update&Backup" is the culprit but I do not know whether it is the problem or not. I have an X96 mini and I did not encounter this issue in the earlier version of the FW.
I do have a workaround, since we only need to use "Update&Backup" once, just format the messed-up SD card and do it again -- your next image will work. I've tried this with multiple versions for the past week.