@Gh0ster 

Hello.

So today, I took NVR from IT enclosure and I disassembly case of NVR. Was working fine for couple hours with "Bad Sector Detection" turned on full scan - it was working fine from 7 am to 12 am when one worker checked notification about motion detection and device starts to beeping. After 5 seconds it dies and app send notification about "no hard drive detected". Next step was force reboot, put HDD in bad sector full scan... And it's working till now. I will gonna check it on Today evening if it's working fine. Maybe it could be ground failure.

  @Gh0ster 

So little update.

Earthing is fixed and fit properly. IT enclosure is grounded to PE from main switchboard by 10mm2 yellow-green insulated copper wire, also all devices inside are grounded by 1,5mm2 copper wire, and UPS is also grounded to enclosure by 6mm2 copper wire.

1st NVR is still connected inside of enclosure while 2nd is temporarily connected on desk. 

I don't know what is going on, because now 2nd is fixed and working properly for 5 days while 1st one (connected and earthed in IT case) is continuously turning offline - I also tried many times manual reboot using VIGI app and Security Manager and NVR stays offline - only power unplug is working with it. Tomorrow I will gonna call TP-LINK support for help and maybe for replacement of both NVR's.

I will tell you what they will propose.

  @Gh0ster 

So after 3 days - NVR's goes offline. So I thought it will be power supply (I had one extra power cord) so I've changed one power cord to another (from 1008 they are the same) and another 2 days of continuous working without failure till today! Both NVR'S are offline.

So here are steps that I tried now:

1. Download from TP-LINK support both firmware the oldest and newest firmware versions,

2. Connect external drive like pendrive (32gb works perfectly NTFS),

3. Export all settings on external drive,

4. Install oldest firmware from external drive,

5. After reboot - install newest firmware from external drive,

6. Make sure all settings are same as before downgradeing/upgrading - if not import them from external drive,

7. Next couple days of testing.

I think there could be one more thing that can make error in system which is: no hard drive failure and then device goes to offline - I'm 90% sure it is because of my WD purple 10 TB HDD have more disk/dishes than other HDD's with lower capacity. Also spin-up time is on 1st HDD= ~574, 2nd HDD= ~618 - so for me it means that software is loading up much faster than HDD and somehow it shuts down spinning up process - because its too long than it should be.

Maybe support should try to make another version with updated code for each type of HDD's with higher capacity and more disks/dishes - to wait X seconds untill drive spin-up and will be visible by software. By this I mean that booting system should take a little bit longer time than it is doing now - fine it's good to have system running after couple seconds but for all those issues with hard drives - it drives crazy. There should be auto-check script which will continuously every X seconds try to recognise HDD that wasn't recognized - because of longer spin-up time. And also there should be option to force reboot in every case! Now reboot is working only when everything is working perfectly! If NVR find out that there is no HDD installed - NVR goes offline and completely unusable and there is no option to reboot - only removing power cord works! 

We will see in couple days what is going on. If there will be more failures I will ask my dealer to exchange NVR'S for new ones.