When setting up a new Solus virtual machine with the new 3.9999 iso, I couldn't verify the Solus-3.9999-Budgie.sha256sum:
$ gpg --verify Solus-3.9999-Budgie.sha256sum.sign gpg: Signature made Thu 20 Sep 2018 16:10:18 BST gpg: using RSA key 96B4A0291094A86A2B7E3367DD672FE9A2BE5892 gpg: Good signature from "Joshua Strobl (Personal) <joshua@stroblindustries.com>" [unknown] gpg: WARNING: This key is not certified with a trusted signature! gpg: There is no indication that the signature belongs to the owner. Primary key fingerprint: 96B4 A029 1094 A86A 2B7E 3367 DD67 2FE9 A2BE 5892 gpg: WARNING: not a detached signature; file 'Solus-3.9999-Budgie.sha256sum' was NOT verified!