@jeff.ohrstrom Thank you for your reply.
I think our issue is the same issue as described in the GitHub link.
I use httpd-2.4.37-56 on RedHat 8.8. The URL when I launch the Shell Access is https://ondemand.fugaku.r-ccs.riken.jp/pun/sys/shell/ssh/login.fugaku.r-ccs.riken.jp.
Another information is that the above environment is a production environment, and we also have a test environment, where Shell Access works, and the configuration files are almost the same in both environments, but the software environment is a bit different. On the test environment httpd-2.4.37-65 on Rocky Linux 8.10 are used. The URL is https://ondemand-test.fugaku.r-ccs.riken.jp/pun/sys/shell/ssh/login.fugaku.r-ccs.riken.jp.
Thanks,