Reply #2, #6, and #9 showed htop with the lighttpd process having taking a large amount of CPU time, so I wonder if that is contributing.
On the off chance that there is some interaction with openssl KTLS on your large system, which might also have TLS acceleration hardware used by openssl drivers, please *test* with KTLS disabled in lighttpd, as lighttpd mod_openssl uses KTLS by default on Linux and FreeBSD, when available. lighttpd.conf: `ssl.openssl.ssl-conf-cmd += ("Options" => "-KTLS")`, or you can *test* disabling KTLS system-wide on FreeBSD `sysctl kern.ipc.tls.enable=0`
On the off chance that there is some interaction with openssl KTLS on your large system, which might also have TLS acceleration hardware used by openssl drivers, please *test* with KTLS disabled in lighttpd, as lighttpd mod_openssl uses KTLS by default on Linux and FreeBSD, when available. lighttpd.conf: `ssl.openssl.ssl-conf-cmd += ("Options" => "-KTLS")`, or you can *test* disabling KTLS system-wide on FreeBSD `sysctl kern.ipc.tls.enable=0`