I believe I am in the same situation as others here. Let me know if this is different. I have a letsencrypt cert for my fqhn.com that I can connect to from outside local LAN (I host this machine on my local LAN). I have a local LAN dns that points to the same fqhn.com but IP is translated to a local IP Address for connections. Other devices (Linux or OpenSSL, curl) can connect to my fqhn.com on local LAN fine. when I try any apple device on wifi/local LAN I get an error “Safari can’t open the page because it couldn’t establish a secure connection to the server”. When I turn wifi off on one of these devices which is an iPhone and use my ISP to connect to fqhn.com, the website loads fine. I assume this is same issue where the cert is no longer trusted.