Rsync error in file IO (code 11) at receiver.c(374) Broken pipe (32)

Nextcloud version: 20.0.4.0
Operating system and version: NextCloudPi v1.35.0

Hi, I have a nextcloudpi and I want to make a sync on a second raspberry. I followed this guide: Configuration-Reference | NextCloudPi Documentation

In summary:
I activated root account on nextcloudpi
I created a specific account on the second raspberrypi, with permission to write.
root from nextcloudpi is able to ssh (without password) to the second raspberry account.

If I test it with
rsync -e 'ssh -p 22' -aAv /home/pi/ b@B:/path/to/your/backup/
everything seems ok, but when I use nextcloud interface, it doesn’t work:

[ nc-rsync ] (Wed Apr 14 18:58:41 BST 2021)
Maintenance mode enabled
Nextcloud is in maintenance mode - no apps have been loaded

rsync: readdir("/mnt/backupdisk2/nextcloud/myCloudDrive/appdata_ocrnfg5r4p1o/preview/39343"): Input/output error (5)
rsync: recv_generator: failed to stat "/mnt/backupdisk2/nextcloud/myCloudDrive/appdata_ocrnfg5r4p1o/preview/39343/192-256.jpg": Input/output error (5)
rsync: recv_generator: failed to stat "/mnt/backupdisk2/nextcloud/myCloudDrive/appdata_ocrnfg5r4p1o/preview/39343/256-256-crop.jpg": Input/output error (5)
rsync: recv_generator: failed to stat "/mnt/backupdisk2/nextcloud/myCloudDrive/appdata_ocrnfg5r4p1o/preview/39343/256-341.jpg": Input/output error (5)
rsync: recv_generator: failed to stat "/mnt/backupdisk2/nextcloud/myCloudDrive/appdata_ocrnfg5r4p1o/preview/39343/480-640-max.jpg": Input/output error (5)
rsync: recv_generator: failed to stat "/mnt/backupdisk2/nextcloud/myCloudDrive/appdata_ocrnfg5r4p1o/preview/39343/64-64-crop.jpg": Input/output error (5)
IO error encountered -- skipping file deletion
rsync: recv_generator: failed to stat "/mnt/backupdisk2/nextcloud/myCloudDrive/appdata_ocrnfg5r4p1o/preview/39349/256-192.jpg": Input/output error (5)
rsync: recv_generator: failed to stat "/mnt/backupdisk2/nextcloud/myCloudDrive/appdata_ocrnfg5r4p1o/preview/39349/256-256-crop.jpg": Input/output error (5)
rsync: recv_generator: failed to stat "/mnt/backupdisk2/nextcloud/myCloudDrive/appdata_ocrnfg5r4p1o/preview/39349/341-256.jpg": Input/output error (5)
rsync: recv_generator: failed to stat "/mnt/backupdisk2/nextcloud/myCloudDrive/appdata_ocrnfg5r4p1o/preview/39349/64-64-crop.jpg": Input/output error (5)
rsync: recv_generator: failed to stat "/mnt/backupdisk2/nextcloud/myCloudDrive/appdata_ocrnfg5r4p1o/preview/39349/640-480-max.jpg": Input/output error (5)
rsync: write failed on "/mnt/backupdisk2/nextcloud/myCloudDrive/appdata_ocrnfg5r4p1o/preview/3132/2048-1536-max.jpg": Read-only file system (30)
rsync error: error in file IO (code 11) at receiver.c(374) [receiver=3.1.3]
rsync: [sender] write error: Broken pipe (32)
Maintenance mode disabled

After this error I cannot access to the harddrive on the second raspberry, and I need to restart it:

domi84@raspberrypi:~ $ cd /mnt/
domi84@raspberrypi:/mnt $ cd backupdisk2/
domi84@raspberrypi:/mnt/backupdisk2 $ ls
ls: reading directory '.': Input/output error
domi84@raspberrypi:/mnt/backupdisk2 $ 

Some extra info:

Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/root       15022248 1287872  13091836   9% /
devtmpfs           57424       0     57424   0% /dev
tmpfs              90400       0     90400   0% /dev/shm
tmpfs              90400    2656     87744   3% /run
tmpfs               5120       4      5116   1% /run/lock
tmpfs              90400       0     90400   0% /sys/fs/cgroup
/dev/mmcblk0p1    258095   48676    209420  19% /boot
tmpfs              18080       0     18080   0% /run/user/1001
/dev/sda1      229701520 1868924 216094712   1% /mnt/backupdisk2
domi84@raspberrypi:/mnt/backupdisk2 $ sudo lsblk -o UUID,NAME,FSTYPE,SIZE,MOUNTPOINT,LABEL,MODEL
UUID                                 NAME        FSTYPE   SIZE MOUNTPOINT       LABEL  MODEL
                                     sda                223.6G                         SATA_SSD
b7a89b81-76d2-4a31-84d8-f4f44170850e └─sda1      ext4   223.6G /mnt/backupdisk2    

what am I doing wrong?

So, it seems a rsync bug (if I understood properly).
It doesn’t work with this:

rsync -e 'ssh -p 22' --progress -aAv Fotografia/ domi84@192.168.1.9:/mnt/backupdisk/folder_test/

But it does work with this (that should be an equivalent command):
rsync -e 'ssh -p 22' --progress -rltzuv Fotografia/ domi84@192.168.1.9:/mnt/backupdisk/folder_test/

Source: Copy from HD to USB | TrueNAS Community

But of course I cannot modifiy nextcloud sync script…So don’t know what to do…