The current master branch of gnupg (commit 24ae5af102cb53bd7abfb9f25aca93debb785a2f) displays [User ID not found] when attempting to import a key:
$ gpg --import damien.asc gpg: key A8DC7067E25EFBABB: 17 signatures not checked to due to missing keys gpg: key A8DC7067E25EFBABB: public key "[User ID not found]" imported gpg: Total number processed: 1 gpg: imported: 1
It also happens when the imported key is already present in the keyring:
$ gpg --import damien.asc gpg: key A8DC7067E25FBABB: 17 signatures not checked due to missing keys gpg: key A8DC7067E25FBABB: "[User ID not found]" not changed gpg: Total number processed: 1 gpg: unchanged: 1
This is independent of the actual key imported.
The bug is not present in GnuPG 2.2.4 and also not present in tag gnupg-2.3-base, so it must have been introduced somewhere in the 2.3 branch.