"Could not read system exclude file" after reboot

Having a problem with a single Windows 10 desktop. When we install the desktop sync client, it’s fine and syncs. But as soon as she restarts the machine for any reason, she gets the “Could not read system exclude file” warning, and syncing fails.

I’m told this began when she somehow doubled the number of times she’d configured to sync with a particular server. The tech uninstalled the client entirely and reinstalled, and now we have this. Multiple uninstalls/reinstalls have not worked. We have tried both the latest stable client and the latest daily-release version, same effect on both.

The server on the other end is a Linux machine running NextCloud 16.0.4. Grateful for any advice. Where is the desktop sync client stored on Windows, for example?