In TMM Monitoring with username / password doesn't work

I did enable monitor logging already. I do see the 'GET' command:

(monitor_and_params): /Common/pool_monitor: IP_TOS= 0, RECVDISABLE= , USERNAME= domain\username, SEND= GET /tfs/_apis/health HTTP/1.1\r\nHost: pool\r\n, RECV_I= HTTP/1.1 200 OK, PASSWORD= <sensitive data redacted>,  [ tmm?=false td=true tr=false addr=::ffff:10.202.4.216:80 srcaddr=none mon=/Common/pool_monitor ]

But the only response I see is:

Probing monitor instance '/Common/pool_monitor' '/Common/node' 80 [ tmm?=false td=true tr=false addr=::ffff:10.202.4.216:80 srcaddr=none ]
(main_loop [next_ping]) Closing logging file /var/log/monitors/Common_pool_monitor-Common_node-80.log
(_do_ping): time to ping, now=[1611242324.368594][2021-01-21 16:18:44], status=UNKNOWN [ tmm?=false td=true tr=false addr=::ffff:10.202.4.216:80 mon=/Common/pool_monitor fd=-1 pend=0 #conn=0 up_intvl=5 dn_intvl=5 timeout=16 time_until_up=0 immed=0 next_ping=[1611242319.368236][2021-01-21 16:18:39] last_ping=[1611242322.638621][2021-01-21 16:18:42] deadline=[1611242340.368236][2021-01-21 16:19:00] on_service_list=True snd_cnt=0 rcv_cnt=0 ]
(_do_ping): probing with tmm [ tmm?=true td=true tr=false tmm_mid=1:0 addr=::ffff:10.202.4.216:80 srcaddr=none ]
(_do_ping): post ping, status=UNKNOWN [ tmm?=true td=true tr=false tmm_mid=1:0 addr=::ffff:10.202.4.216:80 mon=/Common/pool_monitor fd=-1 pend=0 #conn=0 up_intvl=5 dn_intvl=5 timeout=16 time_until_up=0 immed=0 next_ping=[1611242329.368236][2021-01-21 16:18:49] last_ping=[1611242324.3685
94][2021-01-21 16:18:44] deadline=[1611242340.368236][2021-01-21 16:19:00] on_service_list=True snd_cnt=1 rcv_cnt=0 ]
TMM::handle_message(TMA_Message<tma_msg_args_notify>*): tmm monitor indicates service down [ tmm?=true td=true tr=false tmm_mid=1:26 addr=::ffff:10.202.4.216:80 srcaddr=none ]
(main_loop [next_ping]) Closing logging file /var/log/monitors/Common_pool_monitor-Common_node-80.log

I'm used to seeing the actual response string from the server, but in this case, this is the only response I see in the monitoring logfile.