I can see there are lots of discussion on here about post OS5 upgrade.
This is my scenario and I am not a tech expert. I get by.
I have a 4tb MyCloud device about 9 yrs old. Perfect working order. Can’t access on network as not OS5?
Unit went into safe mode, screen says my os is version 1 (out of the box 9 yrs ago?) so I upgrade it through the site to version 3 first. Perfect. But still can’t see on network and cannot manually install Plex server on. So take the OS5 upgrade, all works perfect, set up and go. Within 3 minutes we have fast blinking blue light and can’t access it any way including ping.
4 second reset, boots and goes into safe mode. Says it’s on version 1 and so we go round in circles? The unit does not seem to remember that it’s now OS5. So I extracted all data off and reformatted using WD utilities. 3.92tb drive brand new. Upgraded today, same process but it’s back to blue flashing light and unaccessible. So I accept the unit (motherboard?) is kerput. The drive is perfect so is there a way of still using this as a network drive without the WD dashboard? How can I utilise the hard drive to still store movies and Music on?
Any ideas? Keep it simple please lol 
help!
Small update after some more research!
This MyCloud device is a single bay one which apparently doesn’t support 3rd party apps and the feature to manually add one has gone in OS3.
Have rebooted, done safe mode again, updated to OS3 where it’s very happy. Can log in and out fine and drive is healthy. I have also read I can leave it on OS3 but will not get any updates which suits me fine as the updates seem corrupted anyway?
So my question now is, does anyone now how I can manually get Plex media server onto the drive without upgrading to OS5, which will fail again?
Do you know if your device is a 1st generation or 2nd generation? Are the last two numbers 00 or 10? 00 is 1st generation and 10 is 2nd generation.
My 1st generation OS4 is set up on my home network and is not connected to the internet. It works fine and I can use the Dashboard.
@Colonelkaye
The 1st generation still uses Twonky. I don’t know if Plex will work on it.
Image from mine.
It’s gen 2 as it ends in a 10!
This is the most ridiculous update I have ever written. I watched a YouTube video of a guy who dismantled his single bay MyCloud as a tutorial but at the end, mentioned his unit started working normal when he put back together. So I did the same …………
Hey presto it’s on OS 5, running latest firmware and Plex installed the first time!
Let us know how PLEX works for you on that hardware . . . . I was always under the impression that the 2nd Gen MyClouds really didn’t have the horsepower to run plex effectively.
I am curious on what you fixed by dissassembling the unit 
Well now comes the challenge so kindly explain this to me becaus3 I am starting to think conspiracy!
I had this single bay and I have en ex-ultra2. On the ultra was visible on the OS5 app and on my windows network via explorer. I could download on my laptop and save to the ultra 2 via this method. Worked perfectly for years.
Opened up the single bay, full dismantle and then rebuild. Upgrade to OS3 then OS5 no problem. Noticed in the apps section extra apps that were not there on old rebuilds so waited for usual blue flicker …… nothing. It’s working fine and now visible on windows explore network and I hav3 save a file into it. But now the ultra has vanished and windows cannot detect.
Ultra still plays perfectly on Plex and the app can see it too? So explain that one?
Plex is happily stored on the single bay now but I cannot get Plex to pick the server up as it’s not visible on anything other than windows.
Confused.
OH - - -you have TWO nas units.
Do the NAS units have unique device names?
Are they grabbing unique IP addresses? (I manually assign from the router as a best practice).
Not sure the OS/5 apps like having multiple NAS units on the same user account (I seem to recall this to be a notable limitation)
Yes both of my NAS units have unique names and are now both operating happily on OS5. Unit 1 is a 4tb Single Bay MyCloud and unit 2 is an 8tb Ex-Ultra 2 MyCloud.
Both units are visible on OS5 app on iOS but single bay shows as offline.
Only single bay is visible on my windows network through explorer and I can save to unit 1.
Unit 2 used to be visible on windows network and I was able to save directly to it using my laptop. Since single bay was repaired, unit 2 is not visible.
Plex is installed on both units but Plex only sees unit 2 and plays perfectly.
I cannot get Plex to pick up the single bay as a server.
If this is because you can’t have two NAS units on one network, it’s News to me and I cannot find anything anywhere that describes my mess!
Update: Plex is resolved, I simply had to configure the media server from the NAS device directly by logging in, selecting apps and then configure.
Both NAS devices happily playing Plex to any TV or device on my network.
So why the jimminy crickets can Windows not see it or the app itself (OS5) not see both devices online? Baffled
Probably an issue with NTLM security version of SMB.
I own an a single bay 8 TB and mobile app for iPhone is working right.
