JorgeB

Basically that's it, you just need to assign the new disk before starting the array.

sdj1 wasn't successful, so you shouldn't have run sdj, though it won't matter much, reboot and try running preclear again.

Oct 5 10:07:21 ChrizNAS kernel: FAT-fs (sda1): error, corrupted directory (invalid entries) Connect the flash drive to a PC and run chkdsk.

Doesn't look like a disk problem, wait for the parity2 sync to finish then check/replace cables on that disk and if the emulated disk is mounting and contents look correct you can rebuild on top.

This is a strange one, please check if the permissions are correct after a reboot, if not stop all dockers/VMs and boot in safe mode, if now they are correct start enabling everything to try and find the culprit, if they are correct at boot again see if you can find if they go wrong after using some docker/VM, etc.

Disable WSD (Settings -> SMB) and see if it makes any difference, but at most that should cause SMB issues, not crash he server.

btrfs is detecting data corruption, you should run memtest.

^This

You can contact support, they will replace the flash drive for you.

Click on the flash drive and add it to the default boot option, like this:

Then reboot.
 
P.S. just noticed thy I linked the same post twice above, if you need to suppress the error it's here.

btrfs raid5/6 has been experimental for many years, I've been using in multiple pools without issues for many years, but there are some known issues still, though most serious ones have been fixed, so make sure you have good backups, but you should have good backups anyway.
 
For now you can use the ZFS plugin to create and manage pools, it's expected that official support will be present in Unraid's next release (v6.12)

This suggests notifications are not going out due to bad credentials, go to Settings -> Notification Settings -> SMTP Settings and check/test config.

There are no NTP servers configured, set pool.ntp.org as NTP server 1.

Run xfs_repair again without -n or nothing will be done, if it asks for it use -L.

Correct.

Correct, and check "parity is already valid" before array start, but like mentioned you should update first.

Looks more like a connection/power problem but wait for the SMART test to finish and check the results, or post new diags.

Please post output of
btrfs fi usage  
For some reason SSK_SSK_Storage_DF56419883BF3-0:0 (sda) is being mounted as disk1.

Delete network-rules.cfg and it will be recreated, eth0 will be the one used for management.

https://bugzilla.kernel.org/show_bug.cgi?id=215763

Disk3 is SMR, so it's normal to suffer lower write speeds every few minutes, does it get better if you temporarilly transfer just to the other disks?

Looks like a flash drive problem.

It it still going slow or did it speed up after the 8TB mark? Possibly you have a disk with slow sectors, diskspeed docker might show something.

Negative, just re-assign disk1 and start the array to begin rebuilding.

You can do a new config and re-assign all the disks (Tools -> New config)