This must be a problem with the binding itself - I know that error, it’s probaby the result of the “other side” (pihole?) not respecting the HTTP protocol. There is a way to turn off automatic authentication handling in jetty which gets rid of the problem, but it also means that the binding must handle authentication “manually”. The only other “fix” is to fix the other side - which I guess is out of the question.
A similar situation is discussed (and resolved) here.