I was getting the same issue (I think it was since since upgrading to 384.18 but possibly a coincidence) and the point at which it hangs seems different each time. In example below I left it running for 30 mins but nothing happens and I saw no further log entries
View attachment 24686
disk check script shows output below
Running disk check v2.9, with command 'e2fsck -p' on /dev/sda1
SanDisk4GB: clean, 1868/244800 files, 340245/977408 blocks
Mon Jul 13 12:27:26 IST 2020 Disk check done on /dev/sda1
I then enabled USB 3.0 mode and plugged the usb stick in to the USB 3.0 port, re-ran the nvram-save script and it completed in no time at all, which was the first time it completed for me on this firmware version.