Let's Encrypt certificate renewal issue

Operating system: Debian 9
OS version: Virtualmin 6.16 Webmin 1.973

I have a problem with renewing my Let’s Encrypt certificates.
I realized that some certificates were not renewed automatically.
I have tried renewing the certificate manually and also requesting it from scratch from the control panel.
Everything seems to be fine, no errors are detected but what happens is that looking at the data from the panel the certificate is renewed for 3 months but checking the expiration from the browser or from special online tools the expiration date is the one before renewal.

What do you suggest me to do?

Thank you in advance
Francesco

@fcforum I would suggest you to setup renew option for 2.5 months each, this will give you time of 14 days to troubleshooting any unforeseen issues if raised in future. I think the auto renewal issue / function was fixed in latest virtualmin/webmin release. I am running now on debian 10 and everything works for me so I am not sure if that is os related issue or not, but it should not be, anyway, you should upgrade to debian 10 as 9 riched eol I think (not sure about that as I switched to debian 10 all my machines few months after it was released as stable).