Try some of the other hosts from various places around the world. Maybe whoever's blocking started recently, and the other hosts had gotten their certificates already? Or maybe the system has more than one IP (more common now as many systems have both IPv4 and IPv6 addresses, or at least should) and different hosts are using different ones?
For more information on how geoblocking prevents Let's Encrypt from validating control over your domain, including some links to some test sites, you may want to read through this:
But nobody here is likely to know why your system's connectivity isn't working as well as you think it should.