Why does a site with an SSL certificate from Let's Encrypt open intermittently?

Question

Digital certificates

So on one shared hosting I keep several sites, the main domain _site.ru without SSL, additional 3 donems with SSL, 1st domain with a certificate from comodo 2nd with a certificate from Cpanel inc (Comodo CA) 3rd with a certificate from Let's Encrypt here is the 3rd domain that opens through once it is not available at all, it opens every other time but for a very long time.
what could be the problem?

Answer 1

I join the question. Gives almost always, but the download speed of the certificate is 15-20 seconds.