Can't verify PGP signed mails from DH

Months ago, I checked the tick box to get mails from DH signed (See: As I am using Enigmail with Thuderbird I chose the PGP/MIME option too, (but I’ve tried both options over time).

However the verification of the signature always fails, even if I copy and paste the source of the e-mail and verify it myself using GPG it also fails.

Now, I am wondering if it’s just me, or if there’s something wrong on the signing side of things, so my question is has anyone else managed to verify the DH signatures on their e-mails?