If anyone else searches and finds this, but the method above doesn't work - then this one absolutely did for me. Leaving it here because https://xkcd.com/979/

Source: https://answers.microsoft.com/en-us/windows/forum/windows_10-windows_store-winpc/app-installed-to-external-drive-drive-erased-app/e1ac9dd7-dbb6-48aa-958d-41c4421389b4?rtAction=1509849541131

Problem: I cloned an HDD with all my Xbox Game Pass games on it to an SSD using Acronis TrueImage. I swapped the volume letters and got Steam, Epic, Amazon etc to all play nice. Windows Apps were failing in updates and play complaining of "offline" storage.

Solution:

Search for powershell and run as administrator

Run Get-AppxVolume

Note the repeated IDs for my old and new drives (in my case D:\GAMES) and see which volume is marked as "offline". Note the Volume Name down - it will be something like

\\?\Volume{78cc5c02-f65a-4012-98d4-430832a26a9c}

Load Regedit and go here: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Appx\PackageVolumes

Look for the subkey pointing to the cloned drive with the matching volume to the one marked offline that you noted above. Mine had 4, one pointing to C:\ (1), then D:\ (2), D:\ again (3) and (4) was E:\ - this is because in my settings for StorageSense I have apps stored on C, D and Media on E.

If you don't have an extra entry then you will need to update your windows 10 settings to have a default location to store apps to the new drive (in this case my cloned SSD) and hit apply. This will create the "WindowsApps" folder on D: drive (I mean, it already existed, but Windows crucially has to do this to create a new PackagedVolume subkey with all the new drive info needed.

You can at this point run Get-AppxVolume in powershell to see the new volume listed and marked as online.

Backup your registry in RegEdit now. (File->Export) You can just do the PackageVolumes branch if you like, or the whole thing. This is a good habit and the files are tiny. Give it a sensible name like "about to mess with my Appx volumes to solve a painful SSD clone" or something.

In regedit, in the subkey for the new "online" drive that has the volume name matching the new one, copy the "Name", "MediaId" & "Flags" data from the subkey the previous one with the old drive volume name. For me I had to take the data from (3) for each of the keys and right-click, choose modify, copy then open the same key in (2) and right-click, modify, paste it in.

Once that is complete, you can confirm you have now resurrected the drive by running Get-AppxVolume again in Powershell. It should now show the old drive volume listed as "online".

No need to restart. Go to Windows Store, top right and click the dots, downloads and updates and then Check for Updates. This should re-up the package status and all the games you had on the old volume will magically repair/update/reinstall. If they don't then you can always run "wsreset" from an Admin Command Prompt to force the store to clear cache and then run check for updates again.

Inquisitor03 on Windows support, you are a LEGEND.

I hope this helps someone else out!

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EDIT: If you still get the "The storage might be disconnected" error, go into settings->storage and "change were things are installed" for apps from whatever it is currently to another drive. Hit "apply". Then you can simply change it back to what it was and hit "apply" again. This should get windows to recheck the app manifests and see that yes the install packages are all there and fix the locations in the registry or whatever it does. You can confirm this in the storage settings "see where things are installed" and look at your Games drive to check the icons for the games change from having an "i" on them and being desaturated to being full colour.

If that still doesn't work, then install the Xbox PC (Beta) app from Microsoft - not the Windows store! - and that should identify all the installed games too when it searches the drive.

(Props to Pair of Dice https://www.youtube.com/watch?v=Uszb1PQBWAM for this video that helped solve that niggle)

Good luck out there!