The email has been changed to required since there are two issuers inside. ZeroSSL requires an Email, Let's Encrypt does not. If one fails the other is tried automatically.To keep it simple I required the Email. Just put in whatever
It depends on the provider, all of them are different, and all of the modules are written by different people so they do not all share the same featureset.Best go to https://github.com/caddy-dns and find the provider you are using and open an issue where you also share part of your caddyfile.
This explains a lot. I noticed, that my A-records increased with old IP addresses, since I use Caddy. I deleted old entries by hand on the IONOS dashboard.