Eikon Desktop Data API stopped working after changing to a new user on Eikon terminal

We had our application using the .NET Eikon API running for a period without any problems, but after we switched to another user on the Eikon terminal (using the "Stop Automatic Sign In" shortcut), it suddenly stopped working without any kind of error message.

Initializing the service using 'DataServices.Instance.Initialize' succeeds (and even launches Eikon if it's not already running), but the callbacks given to the DataServices.Instance.TimeSeries.SetupDataRequest are never called, even though the message pump is running (again, the executable that was working yesterday no longer works, so it seems unlikely to be any problem with the code).

We've generated new app/api keys, but since we're using the old data API we don't enter it anywhere when accessing the API. The Eikon terminal is of course running on the same computer, and we're able to look up quotes for the same RICs in the terminal.

Thank you!