Pool imported but empy dataset, missing services, corruption?

Hello, on my TrueNAS Core I have a problem I missed: since one week my periodic snapshot tasks where not running and it seems that on snapshot task locked. A few hours ago I tried to reboot (cleanly) the server and was stuck with that screen:


After a while (15 minutes ?) I cut the power and start again the server.
At reboot it showed many mtaslab_unload messages and seemed to be stuck. I tried some carriage returns and nothing except blank lines. I think I tried CTRL+C and boot sequence went on. But after that it seems that many services did not start (remote syslog, smb sharing for example).
My pool was mounted but some data are missing:

# zfs list
NAME                                                            USED  AVAIL     REFER  MOUNTPOINT
freenas-boot                                                   8.12G  7.26G       64K  none
freenas-boot/.system                                            355M  7.26G     48.5K  legacy
freenas-boot/.system/configs-7c35bc62b22f460fb3766e1c156d5c44   177M  7.26G      177M  legacy
freenas-boot/.system/cores                                       26K  1024M       26K  legacy
freenas-boot/.system/rrd-7c35bc62b22f460fb3766e1c156d5c44      26.3M  7.26G     26.3M  legacy
freenas-boot/.system/samba4                                     545K  7.26G      302K  legacy
freenas-boot/.system/services                                    28K  7.26G       28K  legacy
freenas-boot/.system/syslog-7c35bc62b22f460fb3766e1c156d5c44    150M  7.26G      150M  legacy
freenas-boot/.system/webui                                       28K  7.26G       28K  legacy
freenas-boot/ROOT                                              7.70G  7.26G       29K  none
freenas-boot/ROOT/12.0-U8.1                                     262K  7.26G     1.21G  /
freenas-boot/ROOT/13.0-U4                                       258K  7.26G     1.31G  /
freenas-boot/ROOT/13.0-U5.3                                     258K  7.26G     1.31G  /
freenas-boot/ROOT/13.0-U6.1                                     262K  7.26G     1.30G  /
freenas-boot/ROOT/13.0-U6.2                                     267K  7.26G     1.30G  /
freenas-boot/ROOT/13.0-U6.3                                    7.70G  7.26G     1.30G  /
freenas-boot/grub                                              6.96M  7.26G     6.96M  legacy
vol1                                                           1.90T   516G      132K  /mnt/vol1
vol1/xx                                                   1.90T   516G       92K  /mnt/vol1/xx
vol1/xx/data                                              1.22T   516G     1.22T  /mnt/vol1/xx/data
vol1/xx/dsi                                               1.22M   516G      144K  /mnt/vol1/xx/dsi
vol1/xx/users                                              697G   516G      695G  /mnt/vol1/xx/users

for example vol1/xx/data is empty.

zpool status returns no error, everything seems normal.
I tried to create a snapshot of vol1/xx/data but it remains stuck several minutes.
I tried to access /mnt/vol1/xx/data/.zfs/snaphots but no success.
What could I try to get back last vol1/xx/data (as my replicated snapshots end on Dec 6th) ?