How to resolve sdlReference.dtd not found when opening topic in Oxygen?

I have a user who is getting a FileNotFoundException in Oxygen 23.1.

The exception shows that the sdlReference.dtd file cannot be found in the user's local InfoShare folder.

I have had them try deleting local storage which usually fixes similar issues where the CSS is not found. But the error persists.

Tridion Docs 14 SP4, Oxygen 23.1, Oxygen Connector 14.0.6

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