mod_jk fails to connect to JBoss/Tomcat with 'wrong message format' error

Issue

• We've configured httpd to proxy via mod_jk to JBoss or Tomcat, but its connection attempts persistently fail with errors like the following:

[Wed May 11 06:31:06 2022] [3304605:140413916240000] [error] ajp_connection_tcp_get_message::jk_ajp_common.c (1369): (bankr) wrong message format 0x4854 from 127.0.0.1:10580
[Wed May 11 06:31:06 2022] [3304605:140413916240000] [info] ajp_handle_cping_cpong::jk_ajp_common.c (989): (bankr) awaited reply cpong, not received
[Wed May 11 06:31:06 2022] [3304605:140413916240000] [error] ajp_connect_to_endpoint::jk_ajp_common.c (1101): (bankr) cping/cpong after connecting to the backend server failed (errno=0)