In our log /var/log/sw-cp-server/error_log shows:
2020/02/04 10:39:46 [error] 1535#0: *14 directory index of "/opt/psa/admin/htdocs/" is forbidden, client: 98.118.136.36, server: , request: "GET / HTTP/1.1", host: "plesk.xxxxxxxxx.org:8443"
2020/02/04 10:39:46 [error] 1535#0: *14 open()...