Accessing per-site metas over HTTPS is officially unsupported and known to be broken (Accessing per-site metas gives 403 forbidden from cloudflare-nginx, Untrusted connection when visiting per-site meta over ssl). Yet, the Meta link in the help menu from the top bar has recently become protocol-relative (i.e.
//meta.site.stackexchange.com/), which means it won’t work for people using the regular site over HTTPS.
Other links, such as from the site changer at the top left and from the footer of the mobile site, still explicitly link to
This is more or less the inverse of Losing HTTPS from SO to Meta, which calls for protocol-relative links so that HTTPS users stay on HTTPS. However, this shouldn’t be done before the per-site metas actually work over HTTPS.