After spending most of the week trying to install certificates to HA and getting a number of issues including Certificate revoked, I’ve discovered the issue!
If anyone is using a certificate issued by Trustcor (these include the free ones through the DDNS provider NOIP.com), and now experiencing issues this is the reason:
https://www.washingtonpost.com/technology/2022/11/30/trustcor-internet-authority-mozilla/