FYI, if I remove

ClientSecurity.INSECURE_LOCALHOST_ALLOWED

the problem goes away, but then I'm getting this error when I try to use the client:

Error: 14 UNAVAILABLE: No connection established. Last error: Error: 4008100502000000:error:0A00010B:SSL routines:tls_validate_record_header:wrong version number:ssl/record/methods/tlsany_meth.c:81