Customer is using RHEL 8 Httpd and is experiencing a known issue [1] for Httpd v2.4.x. Note that a potential fix [2] has been referenced on the aforementioned bug report. Currently the workaround seems to be to disable module mod_xml2enc.

[1]
https://bz.apache.org/bugzilla/show_bug.cgi?id=64339
https://httpd.apache.org/docs/2.4/mod/mod_proxy_html.html (see Known issues)

[2]https://svn.apache.org/viewvc?view=revision&revision=1884505