401 Unauthorized after token refresh with C# SDK

Getting 401 errors immediately after the refresh token logic runs in our C# desktop app. The new access token looks valid in debug but the API rejects it, suspecting a clock skew issue between our server and Genesys. Here is the config: ClientOptions = new ClientOptions { DefaultBaseUri = new Uri("https://api.mypurecloud.com"), ClockSkew = TimeSpan.FromSeconds(60) };