Why does the Moscow Metro block a site with SSL?

Question

Digital certificates

Hello. I would like to know if I installed a certificate from let's encrypt , in browsers everything is normal and correctly displayed, but the client says that in Moscow metro wi fi blocks the site as unsafe, what could be the matter?

Answer 1

I haven’t been to the subway for a long time, but the last time I tried to connect to free wifi there, chrome yelled about replacing the certificate.
on gmail
, it seems to me that your client simply should not trust free wifi, and not letsencrypt certificates

Answer 2

1. letsencrypt distributes free certificates and not everyone considers it a reliable CA
2. Either the metro itself with Wi-Fi stirs up, or there is a "bug"