Blazor Server App - Authentication/_blazor/disconnect - Http Status code 400

[RonaldGHempel]

I have a Blazor server app deployed to Azure, with Azure SignalR as a dependency.
This app has an availability test which is calling a dedicated availability page with no authentication required. The availability test runs every 5 min.
Within the application logs I see a lot of request with http status code 400 as a result for request to Authentication/_blazor/disconnect. This call is meant to tell SignalR that a client is gone, as far as I understood.
I have checked that the configuration meets the suggestions stated here: https://docs.microsoft.com/en-us/aspnet/core/blazor/host-and-deploy/server?view=aspnetcore-3.1

What do I need to change to eliminate the bad requests?

Thank you for your help in advance.