SITUATION
We migrated our old Active Directory "OldAD.ads" to a complete new one "NewAD.ads"
We use InDesign CC2019 (latest Version)

All out file-shares are mounted on client computers with Microsoft DFS-Links.
- Old DFS-Link: \OldAD\DFS\OldShare - The DFS-Links points to a share on our old fileserver: \OldFileServer.OldAD.ads\Share_OLD
All shares on the old fileserver are closed, so the DFS-Links have no destination but are still "available".

• New DFS-Link: \NewAD\DFS\NewShare - The DFS-Links points to a share on our new fileserver: \NewFileServer.NewAD.ads\Share_NEW

Both fileservers hold "their" (Active Directory based) DFS-structure.

Of course, all users open their files on the new fileserver, shares are mounted via the new DFS-structure.

THE REAL STRANGE ERROR
As long as the old fileserver and old Domaincontroller are up, InDesign acts as expected: We open an old document, the windows "missing links in document" comes up, we fix the broken links, the document opens, everything is fine.

BUT when I shut down the fileserver and the last domaincontroller, the following happens: We open an old document (containing links to documents, that were on shares mounted via the old DFS on our old fileserver), InDesign freezes and the mouse pointer circles. I waited up to 30 minutes, nothing happened. And now comes the really strange thing: When I unplug the network cable (no joke), the "missing links in document"-windows comes to front and I can fix the broken links after plugging in the cable again.
When I turn on the old fileserver and domaincontroller again, everything works fine again.

I can reproduce this error on all our 4 InDesign-workstations. The error only appears when the broken path contains a DFS-Link and the link is not available any more - no matter if the "real" share behind the link is available or not.
The InDesign option "Ignore missing links when opening a document" does not affect the error, it happens when the option is set or not.