GnuPG 2.3 may produce incompatible Ed25519 signature.
That's because the signature in Ed25519 is composed by R and S, where:
- R is an EC point
- S is an integer (little-endian)
And R is encoded without the 0x40 in OpenPGP.
In GnuPG 2.2 currently, when it is written out, leading zero-bytes are removed (to avoid malformed MPI in OpenPGP).
When it is read, GnuPG (both of 2.2 and 2.3-beta), recovers this leading zero-bytes.