How to fix an SSL error on a website?

Question

Digital certificates

There is an error on the site in Firefox

Error establishing a secure connection

While loading the page, the connection to ... was interrupted.
The page you are trying to view cannot be displayed because the validity of the received data cannot be verified.
Please contact the website owners and inform them of this issue.
Chrome says

ERR_CONNECTION_CLOSED:
SSL connection
failed Error 107 ERR_SSL_PROTOCOL_ERROR

Judging by Yandex Metrica, attendance is 0, which means that the error is not only in my browser, but in everyone. It costs the VestaCP panel to put a certificate through it, it shows:
NOT_BEFORE: Dec 30 23:55:19 2017 GMT
NOT_AFTER: Mar 30 23:55:19 2018 GMT
I.e. It looks like the certificate is still valid.
It is necessary to somehow check something on the server, but how and what to check is not clear. Google gives recipes for fixing this error purely in browsers (check the date, enable TLS)
In the main Apache log:
[Sun Feb 11 00:39:54.036848 2018] [:notice] [pid 6177] mod_ruid2/0.9.8 enabled
[Sun Feb 11 00:39:54.404963 2018] [mpm_prefork:notice] [pid 6177] AH00163: Apache/2.4.10 (Debian) mod_fcgid/2.3.9 OpenSSL/1.0.1t configured -- resuming normal operat$
[Sun Feb 11 00:39:54.464912 2018] [core:notice] [pid 6177] AH00094: Command line: '/usr/sbin/apache2'
[Sun Feb 11 03:55:07.951332 2018] [mpm_prefork:notice] [ pid 6177] AH00171: Graceful restart requested, doing restart
[Sun Feb 11 03:55:08.362213 2018] [:notice] [pid 6177] mod_ruid2/0.9.8 enabled
[Sun Feb 11 03:55:08.367920 2018] [mpm_prefork: notice] [pid 6177] AH00163: Apache/2.4.10 (Debian) mod_fcgid/2.3.9 OpenSSL/1.0.1t configured -- resuming normal operat$
There are only 4 PHP-related errors in the Apache error log for this domain

Answer 1

Check ciphersuites. The error may occur due to excessively clamped cipher suites (only modern ciphers) and an attempt to enter, for example, from Windows XP