Updating the Plesk default certificate causes Apache misconfiguration because configuration files still contain information about outdated certificate files that no longer exist in
# apache2ctl -t AH00526: Syntax error on line 109 of /etc/apache2/plesk.conf.d/server.conf: SSLCertificateFile: file '/opt/psa/var/certificates/cert-QWssIy' does not exist or is empty Action '-t' failed.
This is an internal issue with ID #PPPM-6136 (Updating certificate file causes webserver crash), which is planned to be fixed in future product updates.
As a workaround, reconfigure Apache:
# /usr/local/psa/admin/bin/httpdmng --reconfigure-all