itimpi

Have you checked Settings->Global Share settings that you have not limited which drives can be part of User Shares?
 
You are likely to get better informed feedback if you attach your system’s diagnostics zip file to your next post in this thread.

The SMART report for the drive looks OK.
 
You can rebuild parity to the same drive by using the procedure described here in the online documentation accessible via the ‘Manual’ link at the bottom of the GUI or the DOCS link at the top of each forum page.
 
In terms of what caused the issue difficult to say.  The syslog is only held in RAM and restarts each time Unraid is booted.   If you want persistent syslog that can survive a reboot then you need to enable the syslog server.

That seems a not unusual speed - I suspect initial boost was due to,RAM caching.    Do you have Turbo Write mode enabled (which is likely to even get 70 MB/s).   More information on Unraid array write modes can be found here in the online documentation accessible via the ‘Manual’ link at the bottom of the GUI or the DOCS link at the top of each forum page.

Yes - this is quite normal as it gives best performance.
 
If you are using an Unraid 6.11.x release or earlier then you set any share that should be on it as Use Cache=Only.
If you are using an Unraid 6.12.x release or later then you set the pool as Primary storage and nothing as secondary storage.    You can then take advantage of the Exclusive Share feature to improve performance by bypassing the Fuse layer in Unraid.
 
In both cases if it is a single drive (no redundancy) then you need to make sure regular backups are made (probably to the array) and the VM Backup plugin can help with this.   You could also use a multi-drive pool to have built-in redundancy for the pool.

To rebuild the contents of disk2 back onto the same drive you should be using the process documented here in the online documentation accessible via the ‘Manual’ link at the bottom of the GUI or the DOCS link at the top of each forum page.
 
if you are not sure what to do ask again here but with more detail on what you have tried so far.

Prefer means you want files moved from array->cache.   You need Yes for cache->array.
 
This is explained in the help text built into the GUI for the Use Cache setting.

/the commonest cause of this type of symptom is the flash drive has dropped offline for some reason.   We would need the system diagnostics zip file to confirm that.

What do you have set as the default file system?     It will automatically only be encrypted if that is set to one of the encrypted variants, or you explicitly set it to be encrypted by changing the file system by clicking on the drive (with the array stopped) before formatting it.
 
You may find this section of the online documentation useful if you want to change the file system type (but note that it will wipe any existing content on the drive).

Unraid uses standard Linux file systems, so the drives can always be read there outside Unraid if needed.   Each array drive is a self-contained file system and can be read by itself.

Unraid does not put (or require) anything into the appdata directory.   The fact you have it means it must have been created by something you installed.  

I would check file system on the drives associated with the shares as file system level corruption has been known to cause this sort of issue.

You can make the changes without stopping anything
 
Having said that if you are on the 6.12.x releases you can get the same performance benefit without making any changes to paths by doing the following:
Make sure that Permit Exclusive shares is enabled under Settings->Global Share Settings Set the pool to be primary storage with no secondary storage (equivalent to Cache Only in earlier releases) make sure that all files for the share are on the pool.    You will now be able to activate Exclusive mode in the share settings. with these changes you get the same performance whether you go direct or via the User Share path.

If that was the case then I would consider returning them - they are obviously not new.

Not a comment on your diagnostics, but you want to make sure your UPS is NOT set to run Unraid as long as it can, but is set to initiate a shutdown with plenty of power left.    You also do not want the Unraid server set to automatically power on as soon as power is supplied as it means it can come on before the UPS has a chance to recharge.

You can disable a plugin without actually removing it by renaming the .plg file to have a different extension and rebooting.   It then becomes a matter of trial-and-error.
 
You are likely to get better informed feedback if you attach your system’s diagnostics zip file to your next post in this thread so we can see what plugins you are running.

The only part of the USB drive that really matters is the ‘config’ folder and all its contents as that is where all user settings are stored.   However most people seem to like having the Unraid system files as well.

If the drives were on the LSI controller on the old system and will also be on the new system then order is irrelevant.    Unraid recognises drives by serial number - not by where they are connected.   There is only ever a problem if as part of the upgrade the controller type is changed and this results in the disk getting presented differently to the host.  Most likely to happen when RAID controllers are involved rather than simple HBA ones.

You could use the Dynamic File Manager plogin on the Unraid side to do this I believe as it can mount remote shares.

This means you want files moved TO the flash drive - is this what you want?
 
you might want to check that you have a sensible value for the Minimum Free Space setting for the cache drive and the User Shares

I suggest you follow the procedure documented here in the online documentation to rewrite the system files.
 

Unraid has to format its disks to get them correctly partitioned and formatted (which wipes any existing contents).
 
you need at least 1 drive with no content to get started.    This can then be added and formatted as the first disk in the Unraid array.    If you then install the Unassigned Devices plugin this will allow you to mount NTFS drives so that you can copy the content off onto the array drive.   The Dynamix File Manager plugin can help with this.  Once the drive has all its content removed the drive can then be added to the Unraid array to give additional space.   Repeat as many times as needed.
 

You can check that the file /etc/cron.d/root contains entries for those.   If not trying making a change on the User Scripts settings page and apply it to try and regenerate the entries.

You might want to delete (or rename) the config/vfio.cfg file on the flash drive.    There is a good chance that with a new motherboard the device ID's for passed through devices are different.

It is not certain from your description if it is the new drive you have just added or not,  At this point I would suggest running a correcting parity check (which should report the same 2 errors as it corrects them), and then run another non-correcting check which should now report 0 errors.  
 
if you still have errors reported then please post your diagnostics. 

Not using standard features as Unraid only supports top level shares
 
Should be able to do it if you are prepared to five under the covers to do manual configuration but this would be error prone.