Restore Corrupt Roaming Profile from Good Local Profile?

When a similar problem happened to me it was simplest to recover from the latest Reflect backup!

Macrium Reflect is a Clone and Drive Image software, you create a bootable USB in the program, Boot off of the Rescue USB and Create an Image file of the HDD that has C: on it and save it to another drive like a USB HDD. Then when the computer won't boot, you boot off of the Rescue USB and restore your Reflect Image.
This is not helpful advice if you never made a Reflect Backup Image to begin with.

As for your profile problem, Windows is loading a Default Profile. When you reboot the computer any saved files will be removed as this profile is only created for you to either Repair or Replace your User Profile.
Delete User Profile in Windows 10

It definitely was *not* a default profile I was seeing, as it contained many (but not all) of the *user-specific* customizations I had already made. Meanwhile, the system seems to have miraculously recovered, When I logged in this morning, I had my roaming profile again. The only change I made which might account for this is that I disabled Azure AD registration in gpedit.msc. It was spamming my event log with 304 and 307 errors, and I have only a local DC, not Azure AD.

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P.S. I forgot to mention above that I had also disabled fast startup. However I rejoiced too soon. The problem is repeatable. If I log on via Ethernet (connected to the same router as the NAS which is serving as DC and file server), the login successfully loads the roaming profile. If I log in via WLAN (on a router separated from the NAS by an additional router), I get the error message about using a local profile.
I presume that this is a timing problem: once I am logged in, I can see all of the mapped drives on the NAS.
Is it reasonable to suppose that the system is trying to load the roaming profile before the network connection is available?
Is there a way to test this hypothesis or, better still, to ensure reliable timing?
Furthermore, why doesn't the local profile look like the roaming profile?
I thought the whole point of a roaming profile was to duplicate it locally for use when the client PC has no connection to the server.

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P.S. I did a little digging in the event log. The recent occurrences do not show:

DETAIL - The network path was not found.

as I expected, but

DETAIL - The process cannot access the file because it is being used by another process.

instead.
This is surprising because at some of these times this was the only client PC running in the domain.

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The User Profile Service Error does not depend on which router I am connected to. It has meanwhile also occurred when I had an Ethernet connection to the same router as the NAS. However, it does occur more often when I am connected via WLAN to a different router. It occurred to me that "The process cannot access the file because it is being used by another process." might be due to the antivirus software scanning the profile on the NAS, so I excluded the roaming profile directories from scanning. Nonetheless, the error continues to appear sporadically. At least the local and roaming profiles meanwhile appear to be in sync.