Hi @ebonsi
a certificate has nothing to do with a timeout.
And Letsencrypt certificates have only domain names, not ip addresses.
But they can be used with working ipv4 and ipv6.
Your ipv6 2600:1700:b310:c2e0::2 doesn't answer - https://check-your-website.server-daten.de/?q=2600%3A1700%3Ab310%3Ac2e0%3A%3A2
Maybe a firewall problem.
Maybe an internal problem of your local network (ipv6 doesn't work). Maybe a wrong / not existing webserver configuration.
Do you have
Listen [::]:80
Listen [::]:443
directives? Works ipv6 internal? Works ping -6 or tracert -6 internal (no idea, if a Mac supports such commands).