Synced folder location configuration stuck

Hello,

I'm helping a friend with a Lightroom Classic problem on Windows: the configuration item "Specify a location for Lightroom's Synced Images" in Preferences/Lightroom Sync is stuck.

What happened is that the drive on which that folder resided died, and is no longer available. The new folder is on a different drive (drive letter) now, but when we attempt to change this configuration, it keeps reverting to the OLD folder location (after showing the dialog "Do you want to move..." and then actually showing a progress bar for this operation).

We temporarily added another drive, giving it the old drive letter and even putting the correct path there, to no avail. Every time we try to change this configuration, it stubbornly reverts to the old drive. Deactivating the checkbox altogether (so that LrC will create it's own "Mobile Downloads" storage file) does not work either. I've also tried resetting all sync settings (Alt-key) and even deleting all synced data. Nothing helps.

Can anyone tell me where this setting is stored and how I can change it (perhaps with a text editor?) or what I can do to reset it?

Thanks

Alex.