Weird nonsesnical 'one type is more general than the other' error

[TheEnbyperor]

Getting mismatched types error despite exactly the same types. Works when called from some areas of project, fails from other areas.

I tried this code:
https://github.com/AS207960/whois-email, function send_mail in client.rs, called from sender.rs line 161.

I expected to see this happen: Works as if called from main.rs line 101

Instead, this happened:

error[E0308]: mismatched types
   --> src/main.rs:104:5
    |
104 |     tokio::task::spawn(async {
    |     ^^^^^^^^^^^^^^^^^^ one type is more general than the other
    |
    = note: expected type `std::ops::FnOnce<(&trust_dns_proto::rr::rdata::mx::MX,)>`
               found type `std::ops::FnOnce<(&trust_dns_proto::rr::rdata::mx::MX,)>`

Meta

rustc --version --verbose:

rustc 1.44.0-nightly (dbf8b6bf1 2020-04-19)
binary: rustc
commit-hash: dbf8b6bf116c7bece2987ff4bd2792f008a6ee77
commit-date: 2020-04-19
host: x86_64-unknown-linux-gnu
release: 1.44.0-nightly
LLVM version: 9.0

[jonas-schievink]

Presumably the same issue as #71723

[TheEnbyperor]

Appears to be so yes.