Can't see size/usage information for system folders

I'm getting close to filling my ~600GB root directory. I know that I can expand it - but in the first instance I'd like to know what's taking up the space.

sudo du and sudo ncdu show:

28G     home18G     var4.1G    swap.img3.6G    usr252M    boot39M     lost+found5.8M    etc4.6M    run76K     tmp56K     root24K     snap16K     opt4.0K    srv4.0K    mnt4.0K    media0       sys0       sbin0       proc0       libx320       lib640       lib320       lib0       dev0       bin

sudo df shows:

Filesystem                              Size  Used Avail Use% Mounted ontmpfs                                   2.0G  4.9M  2.0G   1% /run/dev/mapper/ubuntu--vg-ubuntu--lv       628G  463G  139G  77% /tmpfs                                   9.8G     0  9.8G   0% /dev/shmtmpfs                                   5.0M     0  5.0M   0% /run/lock/dev/sda2                               2.0G  254M  1.6G  14% /boottmpfs                                   2.0G  4.0K  2.0G   1% /run/user/1000

I've run things like autoclean and autoremove - no change.

Any ideas? Thanks!