My website has a really long TTFB, about 10-20 seconds. Here are the results from webpagetest: https://www.webpagetest.org/result/191231_XT_1c7004d39484c32e8e2493c4b4bb75c4/2/details/
The web bytecheck says that the very long task is SSL. But the SSL certificate (letsencrypt) seems to be ok (ssllabs.com/ssltest gives an A grade).
Also I think it is not a code issue, because if I create a new html static page that only contains the word "hello", it also takes several seconds to load. The server doesn't seem to be overload either, the command htop shows a very low CPU and RAM usage.
So, any idea what can be slowing the website?