Comment # 2 on bug 1093836 from Andreas Stieger

(In reply to Manfred Hollstein from comment #0)
>   Enigmail: Error - no matching secret found to decrypt message

This is normally an indication of mixed used of GnuPG 2.0 and 2.2, e.g. as
would happen when sharing a home directory, or when the gpg-agent keeps
running.

> Downgrading to enigmail-1.9.9-9.1 results in a fully working
> MozillaThunderbird/enigmail combination.

Hmm interesting.

> Since openSUSE Leap 15.0 already has enigmail-2.0.2 and gpg2-2.2, I booted
> into Leap 15.0 to run the same test opening the exact same e-mail, and there
> it works as expected.

Can you please cross-check you can decrypt the item with plain gpg 2.0 cli?