I created an account to +1 this issue. We recently upgraded to 5.3.24 and started seeing the same errors.

Proget: 5.3.24
Category: Web
Message: An error occurred in the web application: Invalid username or password.
Details: URL: https://our-host/nuget/our-org/
Referrer: (not set)
User: (unknown)
User Agent: NuGet Command Line/5.8.1 (Microsoft Windows NT 10.0.19041.0)
Stack trace: at Inedo.Web.InedoHttpModule.AuthenticateRequestAsync(HttpApplication app)
at Inedo.Web.InedoHttpModule.ProcessBegin(Object sender, EventArgs e, AsyncCallback cb, Object extraData)
at System.Web.HttpApplication.AsyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step)
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

The worst part is the errors are not actually 'logged'. They are written to proget's database which only retains the last 1000 entries per category. Extremely hard to debug on our end.