Ran into my Account being paused for my DIY RaspberryPi GO server.
It worked fine for a few years but suddenly it stopped working.
After i set AAAA record to my IPv6 address in my Strato DNS settings AND i unlocked my being Paused it worked again 
It did work for 2 years having only my A record set to my IPv4 address.
I am not sure but maybe setting the AAAA fixed the issue.
Just create this topic for reference.
Pausing happens because your certificate has repeatedly failed to renew, hundred or thousands of times.
Let's Encrypt will use an AAAA record pointing to an IPv6 address in preference to an A record pointing to an IPv4 address, and that's how it's been for many years.
Most likely you either added an invalid AAAA record yourself, or you switched DNS hosting/registar etc and they added a fake AAAA record pointing to their own domain parking (which is very common). Either way if you declare an AAAA knowingly or not, it has to be correct, and forwarding to your target server etc has to work, or HTTP domain validation will start to fail.