Ok, now I have another issue:
The SSL certificate for the panel won't renew.
Running the cron debug I get the following:
root@server:~# php /var/www/html/froxlor/scripts/froxlor_master_cronjob.php --force --debug
[information] TasksCron: Searching for tasks to do
[information] TasksCron: Task10 started - setting filesystem quota
sh: 1: /usr/sbin/repquota: not found
[information] Running Let's Encrypt cronjob prior to regenerating webserver config files
[information] Checking for LetsEncrypt client upgrades before renewing certificates:
[Sun Aug 1 13:37:42 AEST 2021] Already uptodate!
[Sun Aug 1 13:37:42 AEST 2021] Upgrade success!
[Sun Aug 1 13:37:42 AEST 2021] Installing cron job
2 0 * * * "/root/.acme.sh"/acme.sh --cron --home "/root/.acme.sh" > /dev/null
[information] Updated Let's Encrypt certificate for <URL1>
[information] Updated Let's Encrypt certificate for <URL2>
[information] Updated Let's Encrypt certificate for <URL3>
[information] Updated Let's Encrypt certificate for <URL4>
[information] Updated Let's Encrypt certificate for <URL5>
[information] Updated Let's Encrypt certificate for <URL6>
[information] Updated Let's Encrypt certificate for <URL7>
[information] Updated Let's Encrypt certificate for <URL8>
[information] Let's Encrypt certificates have been updated
[information] apache::createIpPort: creating ip/port settings for <IP address>
[notice] <IP address>:80 :: namevirtualhost-statement no longer needed for apache-2.4
[debug] <IP address>:80 :: inserted vhostcontainer
[information] apache::createIpPort: creating ip/port settings for <IP address>
[debug] System certificate file "/etc/apache2/apache2.pem" does not seem to exist. Disabling SSL-vhost for "<panel URL>"
[debug] System certificate key-file "/etc/apache2/apache2.key" does not seem to exist. Disabling SSL-vhost for "<panel URL>"
[error] <panel URL> :: empty certificate file! Cannot create ssl-directives
[debug] <IP address> :: inserted vhostcontainer
[information] apache::createVirtualHosts: creating vhost container for domain 14, customer <Customer2>
[information] apache::createVirtualHosts: creating vhost container for domain 9, customer <Customer1>
[information] apache::createVirtualHosts: creating vhost container for domain 4, customer <Customer1>
[information] apache::createVirtualHosts: creating vhost container for domain 16, customer <Customer2>
[information] apache::createVirtualHosts: creating vhost container for domain 10, customer <Customer1>
[information] apache::createVirtualHosts: creating vhost container for domain 8, customer <Customer1>
[information] apache::createVirtualHosts: creating vhost container for domain 6, customer <Customer1>
[information] apache::createVirtualHosts: creating vhost container for domain 18, customer <Customer1>
[information] apache::writeConfigs: rebuilding /etc/apache2/sites-enabled/
[information] apache::writeConfigs: rebuilding /etc/apache2/htpasswd/
[information] apache::writeConfigs: rebuilding /etc/apache2/sites-enabled/
[information] Froxlor\Cron\Http\Apache::reload: reloading Froxlor\Cron\Http\Apache
[notice] Checking system's last guid
I can't access the panel anymore now because secure connection cannot be made. I can't figure out how to access via the unsecured HTTP protocol instead, but I'm thinking to disable and reenable LetsEncrypt from within the panel that might sort this out. Any ideas?