It's not the caldav/carddav services. I just noticed the same problem and I don't have those services enabled.
If you just point your browser at https://localhost:8443 you'll see a web management interface for Server itself. Nothing there is actually useful, but that's another story.
It seems to be coming from here:
downsample:~>sudo lsof -i tcp:8443
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
httpd 10449 root 13u IPv6 0x2233e860f31fe631 0t0 TCP *:pcsync-https (LISTEN)
httpd 10472 _www 13u IPv6 0x2233e860f31fe631 0t0 TCP *:pcsync-https (LISTEN)
httpd 10473 _www 13u IPv6 0x2233e860f31fe631 0t0 TCP *:pcsync-https (LISTEN)
httpd 10474 _www 13u IPv6 0x2233e860f31fe631 0t0 TCP *:pcsync-https (LISTEN)
httpd 10476 _www 13u IPv6 0x2233e860f31fe631 0t0 TCP *:pcsync-https (LISTEN)
httpd 10477 _www 13u IPv6 0x2233e860f31fe631 0t0 TCP *:pcsync-https (LISTEN)
httpd 10710 _www 13u IPv6 0x2233e860f31fe631 0t0 TCP *:pcsync-https (LISTEN)
downsample:~>ps ax | grep httpd
10449 ?? Ss 0:00.13 /usr/sbin/httpd -D FOREGROUND -f /Library/Server/Web/Config/Proxy/apache_serviceproxy.conf -E /private/var/log/apache2/service_proxy_error.log
10453 ?? Ss 0:00.16 /usr/sbin/httpd -D FOREGROUND -f /Library/Server/Web/Config/apache2/services/ACSServer.conf -E /var/log/apache2/services/ACSServer_error_log
10471 ?? S 0:00.01 /usr/sbin/httpd -D FOREGROUND -f /Library/Server/Web/Config/apache2/services/ACSServer.conf -E /var/log/apache2/services/ACSServer_error_log
10472 ?? S 0:00.14 /usr/sbin/httpd -D FOREGROUND -f /Library/Server/Web/Config/Proxy/apache_serviceproxy.conf -E /private/var/log/apache2/service_proxy_error.log
10473 ?? S 0:00.15 /usr/sbin/httpd -D FOREGROUND -f /Library/Server/Web/Config/Proxy/apache_serviceproxy.conf -E /private/var/log/apache2/service_proxy_error.log
10474 ?? S 0:00.09 /usr/sbin/httpd -D FOREGROUND -f /Library/Server/Web/Config/Proxy/apache_serviceproxy.conf -E /private/var/log/apache2/service_proxy_error.log
10476 ?? S 0:00.16 /usr/sbin/httpd -D FOREGROUND -f /Library/Server/Web/Config/Proxy/apache_serviceproxy.conf -E /private/var/log/apache2/service_proxy_error.log
10477 ?? S 0:00.06 /usr/sbin/httpd -D FOREGROUND -f /Library/Server/Web/Config/Proxy/apache_serviceproxy.conf -E /private/var/log/apache2/service_proxy_error.log
10710 ?? S 0:00.12 /usr/sbin/httpd -D FOREGROUND -f /Library/Server/Web/Config/Proxy/apache_serviceproxy.conf -E /private/var/log/apache2/service_proxy_error.log
11677 s000 S+ 0:00.00 grep httpd
If you look in /Library/Server/Web/Config/Proxy/apache_serviceproxy.conf you'll see apache httpd configured to listen on a bunch of ports: 80, 443, 8008, 8800, 8443, 8843.
Editing that .conf file, commenting out the "Listen 8443" line, and "sudo killall httpd" seems to keep it off of 8443. I had to do the same thing for 8843 which the unifi controller apparently also wants. After that, and waiting a while (maybe for sockets in CONN_WAIT to close), I was able to start the unifi controller. Hopefully this stays fixed.