SSL Certs are not auto-renewing -> log error: "Another instance of Certbot is already running"

SSL Certs are not auto-renewing (for all of my domains).

So I went into the WebGUI and tried to manually renew the SSL Certificates

Manual renewal worked for one domain, and then from the second domain that had expired, when I choose "renew now" I got the error in a red banner in the webGUI just saying "Internal Error".

So, I checked logs and it contains the following error for all the domains that are not renewed:

"Another instance of Certbot is already running"

Could anyone help, who might have a permanent fix for this?

Full log below:

nginx_proxy_manager    | [5/12/2022] [8:35:50 AM] [SSL      ] › ℹ  info      Renewing Let'sEncrypt certificates for Cert #17: my.domain.com
nginx_proxy_manager    | [5/12/2022] [8:35:50 AM] [SSL      ] › ℹ  info      Command: certbot renew --force-renewal --config "/etc/letsencrypt.ini" --cert-name "npm-17" --preferred-challenges "dns,http" --no-random-sleep-on-renew --disable-hook-validation
nginx_proxy_manager    | [5/12/2022] [8:35:51 AM] [Express  ] › ⚠  warning   Command failed: certbot renew --force-renewal --config "/etc/letsencrypt.ini" --cert-name "npm-17" --preferred-challenges "dns,http" --no-random-sleep-on-renew --disable-hook-validation
nginx_proxy_manager    | Another instance of Certbot is already running.
nginx_proxy_manager    | Ask for help or search for solutions at https://community.letsencrypt.org. See the logfile /tmp/tmp0k76co9u/log or re-run Certbot with -v for more details.
nginx_proxy_manager    |

No source file or test is identified in the report. Begin with the SSL renewal command shown in the logs and trace the WebGUI renewal path; done means reproducing the "Another instance of Certbot is already running" failure and confirming that affected certificates renew without the internal error.