The UID 120 mention has happened before. See:
https://forums.developer.nvidia.com/t/jetson-tx2-change-kernel-without-full-flash/74029/13
…which leads to:
https://askubuntu.com/questions/1037922/ubuntu-18-04-hangs-on-booting-with-message-started-user-manager-for-uid-120-on
Those notes were from some time back with release R32.1, and your JetPack version 4.4 indicates you are using a newer release. Perhaps it is as simple as being out of disk space.