Please fill out the fields below so we can help you better. Note: you must provide your domain name to get help. Domain names for issued certificates are all made public in Certificate Transparency logs (e.g. crt.sh | example.com), so withholding your domain name here does not increase secrecy, but only makes it harder for us to provide help.
$ nmap wave-alchemy.fifteen.dev
Starting Nmap 7.91 ( https://nmap.org ) at 2022-12-12 14:38 PST
Nmap scan report for wave-alchemy.fifteen.dev (18.104.22.168)
Host is up (0.15s latency).
Not shown: 997 filtered ports
PORT STATE SERVICE
22/tcp open ssh
80/tcp open http
443/tcp open https
Nmap done: 1 IP address (1 host up) scanned in 11.00 seconds
I'm more thinking "You had a routing error or perhaps a Man in the Middle attack and the certificate error saved you from leaking information" than that Let's Encrypt had a certificate issue. If the latter would be the case, this Community would have much more threads regarding this issue than this single one