btrfs-balance-least-used: Error during balancing, there may be more info in dmesg: ENOENT, state none

[Massimo-B]

I'm doing a btrfs-balance-least-used in order to optimize free space (Zygo/bees#298):

# btrfs-balance-least-used -u 80 /mnt/local/data/
Loading block group objects with used_pct <= 80 ... found 62
Balance block group vaddr 1303708893184 used_pct 1 ... duration 17 sec total 655
Balance block group vaddr 555222040576 used_pct 32 ...Error during balancing, there may be more info in dmesg: ENOENT, state none

But after some work it fails like this.
In the syslog (grep BTRFS) I can't find much but this:

[kernel] BTRFS info (device dm-2): balance: start -dvrange=1303708893184..1303708893185
[kernel] BTRFS info (device dm-2): relocating block group 1303708893184 flags data
[kernel] BTRFS info (device dm-2): found 1 extents, stage: move data extents
[kernel] BTRFS info (device dm-2): found 1 extents, stage: update data pointers
[kernel] BTRFS info (device dm-2): balance: ended with status: 0
[kernel] BTRFS info (device dm-2): balance: start -dvrange=555222040576..555222040577
[kernel] BTRFS info (device dm-2): relocating block group 555222040576 flags data
[kernel] BTRFS info (device dm-2): found 6650 extents, stage: move data extents
[kernel] BTRFS info (device dm-2): balance: ended with status: -2

Trying a usual balance it also fails after a while:

btrfs balance start -dusage=80 /mnt/local/data/
ERROR: error during balancing '/mnt/local/data/': No such file or directory

Kernel: 6.6.30-gentoo