Oh, yeah 
I see it.
We added .home.arpa to the list of TLDs that we automatically configure tls internal for. We did that because it slightly simplifies config for most users using Caddy.
We didn’t consider that it could be a breaking change for anyone using an CA external to Caddy itself for that TLD! (I’m kinda surprised anyone even does, to be frank).
I think what you’d need to do is explicitly configure tls in each site block instead of using the global acme_ca option unfortunately, because you need to explicitly override the implicit tls internal default.
You can use snippets though which slightly reduces the amount of config. Might look something like this:
(tinyca) {
tls {
ca https://tinyca.home.arpa/acme/acme/directory
}
}
truenas.home.arpa {
import tinyca
reverse_proxy 192.168.9.6
}
...
Sorry for the trouble 