If you see this post twice, I apologize, but I thought this the best place for it.
After no less than 3 unsuccessful attempts to upgrade my existing W10Pro from 1909, it finally "took" less than 2 weeks ago.
Now, no questions please, as I won't be able to give you any helpful answers; it just worked without me doing anything extraordinary.
It's upgraded itself to (verbatim): Version 21H1 (OS Build 19043.1165)
Now, here's what I did differently this time around compared to the previous. Will my method work for you? I have no idea! Here's some basic, essential background info:
1: I had been running Windows 10 Pro version 1909 (OS Build 18363.778) before my very first update to version 2004 OS Build 19041.572 last October.
2: When I rolled back, the version left behind was 1909 (OS Build 18363.1082. This tells me that MS had installed some essential fixes, or something like that.
3: I am in a home environment without a server, and the other two PCs connected (via wire from time-to-time) to the LAN are W7Pro and W8.1Pro.
4: These 3 PCS have mappings to a Synology NAS. The W10Pro machine is the only one with mapping issues.
5: After the multiple upgrades mentioned, it got to the point where only fully powering off the PC would cause the lost mappings. Microsoft at work.
What I did differently – and the same – this time around:
1: Unlike previous occasions, I didn't fully Shut Down my machine for, I think, 4 days after the upgrade. Now usually, I never fully power off my PC, but rather, place it into Hibernation overnight. However, as you can see from my initial post, even logging out and back in caused the mapped drives to permanently disconnect. This was somewhat resolved after the first upgrade to x.1082 and its subsequent rollback, as noted above. What does this tell me? It seems MS was working on the issue that they've never acknowledged – at least on this forum with very annoyed and inconvenienced customers. Shame!
2: Alike the previous upgrade occasions, I immediately installed all available updates after the OS upgrade.
3: That night, after the upgrade, I placed my PC into Hibernation as per usual. I was pleasantly surprised, and very relieved that the mapped drives were still accessible next morning!
4: Like I said, it was a few days before I ventured to fully shut off the machine, if only for a few minutes, but a full power-off nonetheless. When everything came back on, I thought, yeah, it might be fixed. I just don't trust Microsoft!
5: Truth be told, I have lost track of how many days it had been since the upgrade this last time, and yesterday I thought my 10-day rollback window may be closed. Anyway, last night, I opted to do a Shut Down instead of my usual nightly Hibernation. This morning, all my mapped drives were there and accessible! Yes!
If this seeming resolution were to be reversed in a subsequent Microsoft "fix"/update, I will only regard that as a malicious, deliberate act, or gross incompetency, by Microsoft.
6: Finally, to reiterate, with the issue still not acknowledged, yet seemingly resolved, it appears Microsoft was quite aware of this issue and CHOSE TO INCONVENIENCE ITS CLIENTS. Disgusting!
So, you don't have to do anything special. No registry hacks. No scripts and batch files. Simply upgrade to at least the version mentioned at the very top and you may be OK. Who the heck knows!
Bonne chance!