Since https://github.com/NixOS/nixpkgs/commit/2d0a48912550cdc39a64e71d09d2c838973871ad, ACME certificates have been issued using a different set of services. The missinghost.invalid configuration here ended up breaking the nginx startup by making it so no selfsigned certificate was ever generated, getting nginx to die on a missing certificate.
Additonally, also as a result of this ACME rework, Stalwart was waiting on a bunch of nonexistent things and now no longer is