Dear btrfs experts,

Could you please help me sort out the following situation:

btrfs df reports my 100Gb device is almost out of space (which agrees 
with the results produced by the standard "df"):

root@next:/home/support# btrfs fi df /
Data, single: total=82.00GiB, used=78.23GiB
System, DUP: total=32.00MiB, used=16.00KiB
Metadata, DUP: total=1.00GiB, used=153.70MiB
GlobalReserve, single: total=68.45MiB, used=0.00B
root@next:/home/support# df -h /
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda3        96G   79G   16G  84% /

However  when I try to locate files to delete with du that's what I get:

|root||@next||:/home/support# du -hd1 /|
|70M     /boot|
|0| |/dev|
|2||.2G /.snapshots|
|14M     /bin|
|4||.5M /etc|
|2||.5M /home|
|348M    /lib|
|4||.0K /lib64|
|0| |/media|
|0| |/mnt|
|0| |/opt|
|0| |/proc|
|40K     /root|
|2||.7M /run|
|12M     /sbin|
|0| |/srv|
|0| |/sys|
|0| |/tmp|
|566M    /usr|
|5||.0G /var|
|29G     /next|
|38G     /|
|
|
|I.e. almost 40Gb just gone somewhere. Am I doing something wrong? Is 
there a problem or a piece of theory I'm missing? Kindly advice.|
|
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|+++++++++++++++++++++++++++++++++++++|
|root@next:~||#  uname -a|
|Linux next 5.10.0-28-amd64 ||#1 SMP Debian 5.10.209-2 (2024-01-31) 
x86_64 GNU/Linux|
|root@next:~||#  btrfs --version|
|btrfs-progs v5.10.1|
|root@next:~||#  btrfs fi show|
|Label: ||'NEXT_ROOTFS'| |uuid: abc71bdb-c570-461d-a28a-54294a646089|
|||Total devices 1 FS bytes used 78.37GiB|
|||devid    1 size 95.46GiB used 84.06GiB path ||/dev/sda3|
|root@next:~||#  btrfs fi df /|
|Data, single: total=82.00GiB, used=78.22GiB|
|System, DUP: total=32.00MiB, used=16.00KiB|
|Metadata, DUP: total=1.00GiB, used=153.64MiB|
|GlobalReserve, single: total=68.45MiB, used=0.00B|
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